diff --git a/20200109/Tower_of_Hanoi.jpeg b/20200109/Tower_of_Hanoi.jpeg
new file mode 120000
index 0000000000000000000000000000000000000000..a1a794afda08596ffa2f46f278db53455de25b6c
--- /dev/null
+++ b/20200109/Tower_of_Hanoi.jpeg
@@ -0,0 +1 @@
+../common/Tower_of_Hanoi.jpeg
\ No newline at end of file
diff --git a/20200109/bsort-1.c b/20200109/bsort-1.c
new file mode 100644
index 0000000000000000000000000000000000000000..3c02adc72e6a7e702e2c7c68c838fc94cc8ef547
--- /dev/null
+++ b/20200109/bsort-1.c
@@ -0,0 +1,48 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200000);
+  return result;
+}
+
+void sort (char **name)
+{
+  for (int i = 1; name[i]; i++)
+    if (compare (name, i - 1, i) > 0)
+      {
+        char *temp = name[i - 1];
+        name[i - 1] = name[i];
+        name[i] = temp;
+      }
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  sort (name);
+  display (name, -1, -1);
+  return 0;
+}
diff --git a/20200109/bsort-1a.c b/20200109/bsort-1a.c
new file mode 100644
index 0000000000000000000000000000000000000000..348b638843002926f57cdcf1d4fbc9bd88d2a10c
--- /dev/null
+++ b/20200109/bsort-1a.c
@@ -0,0 +1,48 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200000);
+  return result;
+}
+
+void sort (char **name)
+{
+  for (int i = 1; name[i]; i++)
+    if (compare (name, i - 1, i) > 0)
+      {
+        char *temp = name[i - 1];
+        name[i - 1] = name[i];
+        name[i] = temp;
+      }
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Zacharias", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", NULL };
+  sort (name);
+  display (name, -1, -1);
+  return 0;
+}
diff --git a/20200109/bsort-2.c b/20200109/bsort-2.c
new file mode 100644
index 0000000000000000000000000000000000000000..d277be0182a40ecd0c66eaeef94d7aebac6aa542
--- /dev/null
+++ b/20200109/bsort-2.c
@@ -0,0 +1,55 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200000);
+  return result;
+}
+
+void sort (char **name)
+{
+  int sorted = 0;
+  while (name[sorted])
+    sorted++;
+  while (sorted > 0)
+    {
+      for (int i = 1; i < sorted; i++)
+        if (compare (name, i - 1, i) > 0)
+          {
+            char *temp = name[i - 1];
+            name[i - 1] = name[i];
+            name[i] = temp;
+          }
+      sorted--;
+    }
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  sort (name);
+  display (name, -1, -1);
+  return 0;
+}
diff --git a/20200109/bsort-3.c b/20200109/bsort-3.c
new file mode 100644
index 0000000000000000000000000000000000000000..67d0097b913171b4523f4f04b6b6ff494046dabd
--- /dev/null
+++ b/20200109/bsort-3.c
@@ -0,0 +1,58 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200000);
+  return result;
+}
+
+void sort (char **name)
+{
+  int done = 0;
+  int sorted = 0;
+  while (name[sorted])
+    sorted++;
+  while (sorted > 0 && !done)
+    {
+      done = 1;
+      for (int i = 1; i < sorted; i++)
+        if (compare (name, i - 1, i) > 0)
+          {
+            done = 0;
+            char *temp = name[i - 1];
+            name[i - 1] = name[i];
+            name[i] = temp;
+          }
+      sorted--;
+    }
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  sort (name);
+  display (name, -1, -1);
+  return 0;
+}
diff --git a/20200109/bsort-4.c b/20200109/bsort-4.c
new file mode 100644
index 0000000000000000000000000000000000000000..241270a46f4ffa005d252207d769c3c4059ed7e2
--- /dev/null
+++ b/20200109/bsort-4.c
@@ -0,0 +1,57 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200000);
+  return result;
+}
+
+void sort (char **name)
+{
+  int sorted = 0;
+  while (name[sorted])
+    sorted++;
+  while (sorted > 0)
+    {
+      int new_sorted = 0;
+      for (int i = 1; i < sorted; i++)
+        if (compare (name, i - 1, i) > 0)
+          {
+            new_sorted = i;
+            char *temp = name[i - 1];
+            name[i - 1] = name[i];
+            name[i] = temp;
+          }
+      sorted = new_sorted;
+    }
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  sort (name);
+  display (name, -1, -1);
+  return 0;
+}
diff --git a/20200109/hanoi-0.c b/20200109/hanoi-0.c
new file mode 100644
index 0000000000000000000000000000000000000000..83b5f081e33e699f2d5eaa1f858320530e1b2820
--- /dev/null
+++ b/20200109/hanoi-0.c
@@ -0,0 +1,26 @@
+#include <stdio.h>
+
+#define DISKS 4
+
+int n[3], tower[3][DISKS];
+
+void display (void)
+{
+  printf ("\n");
+  for (int i = 0; i < 3; i++)
+    {
+      printf ("tower %d:", i);
+      for (int j = 0; j < n[i]; j++)
+        printf (" %d", tower[i][j]);
+      printf ("\n");
+    }
+}
+
+int main (void)
+{
+  n[0] = 0;
+  n[1] = 0;
+  n[2] = 0;
+  display ();
+  return 0;
+}
diff --git a/20200109/hanoi-1.c b/20200109/hanoi-1.c
new file mode 100644
index 0000000000000000000000000000000000000000..6d005f0b12afa6086afb65e1794fb5c977b474e2
--- /dev/null
+++ b/20200109/hanoi-1.c
@@ -0,0 +1,30 @@
+#include <stdio.h>
+
+#define DISKS 4
+
+int n[3], tower[3][DISKS];
+
+void display (void)
+{
+  printf ("\n");
+  for (int i = 0; i < 3; i++)
+    {
+      printf ("tower %d:", i);
+      for (int j = 0; j < n[i]; j++)
+        printf (" %d", tower[i][j]);
+      printf ("\n");
+    }
+}
+
+int main (void)
+{
+  n[0] = 4;
+  tower[0][0] = 4;
+  tower[0][1] = 3;
+  tower[0][2] = 2;
+  tower[0][3] = 1;
+  n[1] = 0;
+  n[2] = 0;
+  display ();
+  return 0;
+}
diff --git a/20200109/hanoi-2.c b/20200109/hanoi-2.c
new file mode 100644
index 0000000000000000000000000000000000000000..c928c1130539da08d0882249bdffc877d72289b2
--- /dev/null
+++ b/20200109/hanoi-2.c
@@ -0,0 +1,28 @@
+#include <stdio.h>
+
+#define DISKS 4
+
+int n[3], tower[3][DISKS];
+
+void display (void)
+{
+  printf ("\n");
+  for (int i = 0; i < 3; i++)
+    {
+      printf ("tower %d:", i);
+      for (int j = 0; j < n[i]; j++)
+        printf (" %d", tower[i][j]);
+      printf ("\n");
+    }
+}
+
+int main (void)
+{
+  n[0] = DISKS;
+  for (int i = 0; i < DISKS; i++)
+    tower[0][i] = DISKS - i;
+  n[1] = 0;
+  n[2] = 0;
+  display ();
+  return 0;
+}
diff --git a/20200109/hanoi-3.c b/20200109/hanoi-3.c
new file mode 100644
index 0000000000000000000000000000000000000000..4b59c046962c1f79eca315882d93faf6b6c298c1
--- /dev/null
+++ b/20200109/hanoi-3.c
@@ -0,0 +1,44 @@
+#include <stdio.h>
+#include <error.h>
+
+#define DISKS 4
+
+int n[3], tower[3][DISKS];
+
+void display (void)
+{
+  printf ("\n");
+  for (int i = 0; i < 3; i++)
+    {
+      printf ("tower %d:", i);
+      for (int j = 0; j < n[i]; j++)
+        printf (" %d", tower[i][j]);
+      printf ("\n");
+    }
+}
+
+void move (int from, int to, int disks)
+{
+  if (disks == 1)
+    {
+      if (n[from] <= 0)
+        error (1, 0, "trying to move disk from empty tower");
+      if (n[to] > 0 && tower[to][n[to] - 1] < tower[from][n[from] - 1])
+        error (1, 0, "trying to move larger disk on smaller one");
+      tower[to][n[to]] = tower[from][n[from] - 1];
+      n[to]++;
+      n[from]--;
+    }
+}
+
+int main (void)
+{
+  n[0] = DISKS;
+  for (int i = 0; i < DISKS; i++)
+    tower[0][i] = DISKS - i;
+  n[1] = 0;
+  n[2] = 0;
+  move (2, 0, 1);
+  display ();
+  return 0;
+}
diff --git a/20200109/hanoi-4.c b/20200109/hanoi-4.c
new file mode 100644
index 0000000000000000000000000000000000000000..162a5ba7cccedf64bff8ae9a514aaf146088e3a4
--- /dev/null
+++ b/20200109/hanoi-4.c
@@ -0,0 +1,44 @@
+#include <stdio.h>
+#include <error.h>
+
+#define DISKS 4
+
+int n[3], tower[3][DISKS];
+
+void display (void)
+{
+  printf ("\n");
+  for (int i = 0; i < 3; i++)
+    {
+      printf ("tower %d:", i);
+      for (int j = 0; j < n[i]; j++)
+        printf (" %d", tower[i][j]);
+      printf ("\n");
+    }
+}
+
+void move (int from, int to, int disks)
+{
+  if (disks == 1)
+    {
+      if (n[from] <= 0)
+        error (1, 0, "trying to move disk from empty tower");
+      if (n[to] > 0 && tower[to][n[to] - 1] < tower[from][n[from] - 1])
+        error (1, 0, "trying to move larger disk on smaller one");
+      tower[to][n[to]] = tower[from][n[from] - 1];
+      n[to]++;
+      n[from]--;
+    }
+}
+
+int main (void)
+{
+  n[0] = DISKS;
+  for (int i = 0; i < DISKS; i++)
+    tower[0][i] = DISKS - i;
+  n[1] = 0;
+  n[2] = 0;
+  move (0, 2, 1);
+  display ();
+  return 0;
+}
diff --git a/20200109/hanoi-5.c b/20200109/hanoi-5.c
new file mode 100644
index 0000000000000000000000000000000000000000..e04ad85f63fe92e5c15d22646beb9e9107bf78d6
--- /dev/null
+++ b/20200109/hanoi-5.c
@@ -0,0 +1,45 @@
+#include <stdio.h>
+#include <error.h>
+
+#define DISKS 4
+
+int n[3], tower[3][DISKS];
+
+void display (void)
+{
+  printf ("\n");
+  for (int i = 0; i < 3; i++)
+    {
+      printf ("tower %d:", i);
+      for (int j = 0; j < n[i]; j++)
+        printf (" %d", tower[i][j]);
+      printf ("\n");
+    }
+}
+
+void move (int from, int to, int disks)
+{
+  if (disks == 1)
+    {
+      if (n[from] <= 0)
+        error (1, 0, "trying to move disk from empty tower");
+      if (n[to] > 0 && tower[to][n[to] - 1] < tower[from][n[from] - 1])
+        error (1, 0, "trying to move larger disk on smaller one");
+      tower[to][n[to]] = tower[from][n[from] - 1];
+      n[to]++;
+      n[from]--;
+      display ();
+    }
+}
+
+int main (void)
+{
+  n[0] = DISKS;
+  for (int i = 0; i < DISKS; i++)
+    tower[0][i] = DISKS - i;
+  n[1] = 0;
+  n[2] = 0;
+  display ();
+  move (0, 2, 1);
+  return 0;
+}
diff --git a/20200109/hanoi-6.c b/20200109/hanoi-6.c
new file mode 100644
index 0000000000000000000000000000000000000000..1267605f802246e857c32d29cc0a132609cb24ce
--- /dev/null
+++ b/20200109/hanoi-6.c
@@ -0,0 +1,52 @@
+#include <stdio.h>
+#include <error.h>
+
+#define DISKS 4
+
+int n[3], tower[3][DISKS];
+
+void display (void)
+{
+  printf ("\n");
+  for (int i = 0; i < 3; i++)
+    {
+      printf ("tower %d:", i);
+      for (int j = 0; j < n[i]; j++)
+        printf (" %d", tower[i][j]);
+      printf ("\n");
+    }
+}
+
+void move (int from, int to, int disks)
+{
+  if (disks == 1)
+    {
+      if (n[from] <= 0)
+        error (1, 0, "trying to move disk from empty tower");
+      if (n[to] > 0 && tower[to][n[to] - 1] < tower[from][n[from] - 1])
+        error (1, 0, "trying to move larger disk on smaller one");
+      tower[to][n[to]] = tower[from][n[from] - 1];
+      n[to]++;
+      n[from]--;
+      display ();
+    }
+  else
+    {
+      int help = 0 + 1 + 2 - from - to;
+      move (from, help, disks - 1);
+      move (from, to, 1);
+      move (help, to, disks - 1);
+    }
+}
+
+int main (void)
+{
+  n[0] = DISKS;
+  for (int i = 0; i < DISKS; i++)
+    tower[0][i] = DISKS - i;
+  n[1] = 0;
+  n[2] = 0;
+  display ();
+  move (0, 2, DISKS);
+  return 0;
+}
diff --git a/20200109/hanoi-7.c b/20200109/hanoi-7.c
new file mode 100644
index 0000000000000000000000000000000000000000..f71fcdc0c3f66047ee3ad870d019a06eb328050f
--- /dev/null
+++ b/20200109/hanoi-7.c
@@ -0,0 +1,52 @@
+#include <stdio.h>
+#include <error.h>
+
+#define DISKS 5
+
+int n[3], tower[3][DISKS];
+
+void display (void)
+{
+  printf ("\n");
+  for (int i = 0; i < 3; i++)
+    {
+      printf ("tower %d:", i);
+      for (int j = 0; j < n[i]; j++)
+        printf (" %d", tower[i][j]);
+      printf ("\n");
+    }
+}
+
+void move (int from, int to, int disks)
+{
+  if (disks == 1)
+    {
+      if (n[from] <= 0)
+        error (1, 0, "trying to move disk from empty tower");
+      if (n[to] > 0 && tower[to][n[to] - 1] < tower[from][n[from] - 1])
+        error (1, 0, "trying to move larger disk on smaller one");
+      tower[to][n[to]] = tower[from][n[from] - 1];
+      n[to]++;
+      n[from]--;
+      display ();
+    }
+  else
+    {
+      int help = 0 + 1 + 2 - from - to;
+      move (from, help, disks - 1);
+      move (from, to, 1);
+      move (help, to, disks - 1);
+    }
+}
+
+int main (void)
+{
+  n[0] = DISKS;
+  for (int i = 0; i < DISKS; i++)
+    tower[0][i] = DISKS - i;
+  n[1] = 0;
+  n[2] = 0;
+  display ();
+  move (0, 2, DISKS);
+  return 0;
+}
diff --git a/20200109/hanoi-8.c b/20200109/hanoi-8.c
new file mode 100644
index 0000000000000000000000000000000000000000..6d804063531d424a82924a89d85424c33994793b
--- /dev/null
+++ b/20200109/hanoi-8.c
@@ -0,0 +1,52 @@
+#include <stdio.h>
+#include <error.h>
+
+#define DISKS 64
+
+int n[3], tower[3][DISKS];
+
+void display (void)
+{
+  printf ("\n");
+  for (int i = 0; i < 3; i++)
+    {
+      printf ("tower %d:", i);
+      for (int j = 0; j < n[i]; j++)
+        printf (" %d", tower[i][j]);
+      printf ("\n");
+    }
+}
+
+void move (int from, int to, int disks)
+{
+  if (disks == 1)
+    {
+      if (n[from] <= 0)
+        error (1, 0, "trying to move disk from empty tower");
+      if (n[to] > 0 && tower[to][n[to] - 1] < tower[from][n[from] - 1])
+        error (1, 0, "trying to move larger disk on smaller one");
+      tower[to][n[to]] = tower[from][n[from] - 1];
+      n[to]++;
+      n[from]--;
+      display ();
+    }
+  else
+    {
+      int help = 0 + 1 + 2 - from - to;
+      move (from, help, disks - 1);
+      move (from, to, 1);
+      move (help, to, disks - 1);
+    }
+}
+
+int main (void)
+{
+  n[0] = DISKS;
+  for (int i = 0; i < DISKS; i++)
+    tower[0][i] = DISKS - i;
+  n[1] = 0;
+  n[2] = 0;
+  display ();
+  move (0, 2, DISKS);
+  return 0;
+}
diff --git a/20200109/hanoi-9.c b/20200109/hanoi-9.c
new file mode 100644
index 0000000000000000000000000000000000000000..7694b373b7011e96f6be0ad0f00ba54b67086158
--- /dev/null
+++ b/20200109/hanoi-9.c
@@ -0,0 +1,58 @@
+#include <stdio.h>
+#include <error.h>
+
+#define DISKS 64
+
+int n[3], tower[3][DISKS];
+
+void display (void)
+{
+  printf ("\n");
+  for (int i = 0; i < 3; i++)
+    {
+      printf ("tower %d:", i);
+      for (int j = 0; j < n[i]; j++)
+        printf (" %d", tower[i][j]);
+      printf ("\n");
+    }
+}
+
+void move (int from, int to, int disks)
+{
+  if (disks == 1)
+    {
+      if (n[from] <= 0)
+        error (1, 0, "trying to move disk from empty tower");
+      if (n[to] > 0 && tower[to][n[to] - 1] < tower[from][n[from] - 1])
+        error (1, 0, "trying to move larger disk on smaller one");
+      tower[to][n[to]] = tower[from][n[from] - 1];
+      n[to]++;
+      n[from]--;
+      static int counter = 1;
+      if (counter++ >= 100000000)
+        {
+          display ();
+          counter = 1;
+        }
+    }
+  else
+    {
+      int help = 0 + 1 + 2 - from - to;
+      move (from, help, disks - 1);
+      move (from, to, 1);
+      move (help, to, disks - 1);
+    }
+}
+
+int main (void)
+{
+  n[0] = DISKS;
+  for (int i = 0; i < DISKS; i++)
+    tower[0][i] = DISKS - i;
+  n[1] = 0;
+  n[2] = 0;
+  display ();
+  move (0, 2, DISKS);
+  display ();
+  return 0;
+}
diff --git a/20200109/hanoi-9a.c b/20200109/hanoi-9a.c
new file mode 100644
index 0000000000000000000000000000000000000000..55e8d74db6d7284d6db225a6f8f3e08ab4efdc06
--- /dev/null
+++ b/20200109/hanoi-9a.c
@@ -0,0 +1,58 @@
+#include <stdio.h>
+#include <error.h>
+
+#define DISKS 32
+
+int n[3], tower[3][DISKS];
+
+void display (void)
+{
+  printf ("\n");
+  for (int i = 0; i < 3; i++)
+    {
+      printf ("tower %d:", i);
+      for (int j = 0; j < n[i]; j++)
+        printf (" %d", tower[i][j]);
+      printf ("\n");
+    }
+}
+
+void move (int from, int to, int disks)
+{
+  if (disks == 1)
+    {
+      if (n[from] <= 0)
+        error (1, 0, "trying to move disk from empty tower");
+      if (n[to] > 0 && tower[to][n[to] - 1] < tower[from][n[from] - 1])
+        error (1, 0, "trying to move larger disk on smaller one");
+      tower[to][n[to]] = tower[from][n[from] - 1];
+      n[to]++;
+      n[from]--;
+      static int counter = 1;
+      if (counter++ >= 100000000)
+        {
+          display ();
+          counter = 1;
+        }
+    }
+  else
+    {
+      int help = 0 + 1 + 2 - from - to;
+      move (from, help, disks - 1);
+      move (from, to, 1);
+      move (help, to, disks - 1);
+    }
+}
+
+int main (void)
+{
+  n[0] = DISKS;
+  for (int i = 0; i < DISKS; i++)
+    tower[0][i] = DISKS - i;
+  n[1] = 0;
+  n[2] = 0;
+  display ();
+  move (0, 2, DISKS);
+  display ();
+  return 0;
+}
diff --git a/20200109/hello-gtk.png b/20200109/hello-gtk.png
new file mode 120000
index 0000000000000000000000000000000000000000..cca99209d86683a9a3b0f70bbc149780bae10ba6
--- /dev/null
+++ b/20200109/hello-gtk.png
@@ -0,0 +1 @@
+../common/hello-gtk.png
\ No newline at end of file
diff --git a/20200109/hp-2019ws-p4.pdf b/20200109/hp-2019ws-p4.pdf
new file mode 100644
index 0000000000000000000000000000000000000000..12d85b607400d6e182675fc0f82e78202dc118f5
Binary files /dev/null and b/20200109/hp-2019ws-p4.pdf differ
diff --git a/20200109/hp-2019ws-p4.tex b/20200109/hp-2019ws-p4.tex
new file mode 100644
index 0000000000000000000000000000000000000000..3f4a14e0d8fc82d0b78e65837211f62cbf8f41b6
--- /dev/null
+++ b/20200109/hp-2019ws-p4.tex
@@ -0,0 +1,193 @@
+% hp-2019ws-p4.pdf - Labor Notes on Low-Level Programming
+% Copyright (C) 2014, 2015, 2016, 2018, 2019, 2020  Peter Gerwinski
+%
+% This document is free software: you can redistribute it and/or
+% modify it either under the terms of the Creative Commons
+% Attribution-ShareAlike 3.0 License, or under the terms of the
+% GNU General Public License as published by the Free Software
+% Foundation, either version 3 of the License, or (at your option)
+% any later version.
+%
+% This document is distributed in the hope that it will be useful,
+% but WITHOUT ANY WARRANTY; without even the implied warranty of
+% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+% GNU General Public License for more details.
+%
+% You should have received a copy of the GNU General Public License
+% along with this document.  If not, see <http://www.gnu.org/licenses/>.
+%
+% You should have received a copy of the Creative Commons
+% Attribution-ShareAlike 3.0 Unported License along with this
+% document.  If not, see <http://creativecommons.org/licenses/>.
+
+% README: Versuch 16. und 23.1.2020: Objektorientiertes Grafik-Programm
+
+\documentclass[a4paper]{article}
+
+\usepackage{pgscript}
+\usepackage{multicol}
+\usepackage{amsmath}
+\usepackage{sfmath}
+
+\sloppy
+%\pagestyle{empty}
+\newcommand{\sep}{~$\cdot$~}
+\newcommand{\mylicense}{CC-by-sa (Version 3.0) oder GNU GPL (Version 3 oder höher)}
+
+\begin{document}
+
+  \makebox(0,0.005)[tl]{\includegraphics[scale=0.72]{logo-hochschule-bochum-cvh-text-v2.pdf}}\hfill
+  \makebox(0,0)[tr]{\includegraphics[scale=0.5]{logo-hochschule-bochum.pdf}}
+  \par\bigskip\bigskip
+  \begin{center}
+    \Large\textbf{Praktikumsversuch 4: Objektorientiertes Grafik-Programm}
+    \par\medskip
+    \normalsize Hardwarenahe Programmierung\sep
+    Wintersemester 2019/20\sep
+    Prof.~Dr.~Peter Gerwinski
+  \end{center}
+
+  Aufgabe: Schreiben Sie ein GTK+-Programm,
+  mit dem man verschiedene Objekte (z.\,B.\ Rechtecke, Kreise, Dreiecke)
+  in eine Grafik einfügen und nachträglich verändern kann
+  (z.\,B.\ Position, Größe, Farbe).
+
+  (Beispiel: Ich füge zunächst zwei Rechtecke und einen Kreis in eine Grafik ein,
+  wähle anschließend das erste Rechteck aus und ändere dessen Farbe.)
+
+  \bigskip
+
+  Hinweise:
+  \vspace*{-\medskipamount}
+
+  \begin{itemize}
+    \item
+      Das Beispielprogramm \gitfile{hp}{20200109}{objects-5.c} zeigt,
+      wie man in C verschiedenartige Objekte
+      in einem Array von Zeigern verwaltet.
+    \item
+      Das Beispielprogramm \gitfile{hp}{20191205}{gtk-6.c} zeigt,
+      wie man mit Hilfe der GUI-Bibliothek GTK+
+      verschiedene Objekte in ein Fenster zeichnet.
+    \item
+      Das Beispielprogramm \gitfile{hp}{20191205}{gtk-7.c} zeigt,
+      wie man in der GUI-Bibliothek GTK+
+      Tastatur- und Maus-Eingaben entgegennimmt und verarbeitet.
+    \item
+      Das Auswählen eines bereits vorhandenen Objekts geht am einfachsten
+      mittels Tastatur-Eingaben (z.\,B.\ Ziffer 1 für das erste Objekt usw.).
+      Auswahl mit der Maus ist auch möglich, aber schwieriger.
+    \item
+      Mit Hilfe der Funktion \lstinline{gtk_widget_queue_draw()}
+      teilen Sie GTK+ mit, daß Sie ein \lstinline{GtkWidget}
+      neu zeichnen lassen möchten.
+    \item
+      Das Compilieren eines GTK+-Programms
+      (z.\,B.\ \gitfile{hp}{20190114}{gtk-7.c}) geschieht wie folgt:
+      \begin{lstlisting}[style=cmd,gobble=8]
+        gcc $(pkg-config --cflags gtk+-3.0) -Wall -O gtk-7.c \
+            $(pkg-config --libs gtk+-3.0) -o gtk-7
+      \end{lstlisting}
+      (Den Backslash am Ende der ersten Zeile entfällt,
+      wenn Sie den ganzen Befehl in eine einzige Zeile schreiben.)
+  \end{itemize}
+
+  \bigskip
+  \textbf{GTK+ unter GNU/Linux}
+  \begin{itemize}
+    \item
+      Installieren Sie das Entwickler-Paket für GTK+-3,\\
+      z.\,B.\ unter Debian GNU/Linux und darauf basierenden Systemen:
+      \begin{lstlisting}[style=cmd,gobble=8]
+        apt-get install libgtk-3-dev
+      \end{lstlisting}
+  \end{itemize}
+
+  \bigskip
+  \goodbreak
+  \textbf{GTK+ unter MacOS X}
+  \begin{itemize}
+    \item
+      Zuerst den Paketmanager "`Homebrew"' installieren:
+      \begin{lstlisting}[style=cmd,gobble=8]
+        ruby -e "$(curl -fsSL https://raw.githubusercontent.com/
+                              Homebrew/install/master/install)"
+      \end{lstlisting}
+      (Die URL nicht trennen, sondern in einer Zeile schreiben.)
+    \item
+      Danach mit Hilfe von \lstinline[style=cmd]{brew} GTK+ installieren:
+      \begin{lstlisting}[style=cmd,gobble=8]
+        brew install gtk+3
+      \end{lstlisting}
+  \end{itemize}
+
+  \bigskip
+  \goodbreak
+  \textbf{GTK+ unter Microsoft Windows: Cygwin}
+  \begin{itemize}
+    \item
+      Im Cygwin-Setup-Programm die Pakete \file{libgtk3-devel},
+      \file{xorg-server} und \file{dbus-x11} installieren.
+    \item
+      Bevor Sie GTK+-Programme starten können,
+      müssen Sie einmalig den X-Server starten:
+      \begin{lstlisting}[style=cmd,gobble=8]
+        XWin -multiwindow &
+      \end{lstlisting}
+    \item
+      Bevor Sie GTK+-Programme starten können,
+      müssen Sie einmalig pro Shell-Sitzung\\
+      die \lstinline[style=cmd]{DISPLAY}-Variable setzen:
+      \begin{lstlisting}[style=cmd,gobble=8]
+        export DISPLAY=:0.0
+      \end{lstlisting}
+  \end{itemize}
+
+  \bigskip
+  \goodbreak
+  \textbf{GTK+ unter Microsoft Windows: MinGW}
+  \begin{itemize}
+    \item
+      Installieren Sie \file{MSYS2} (Installer).
+    \item
+      Installieren Sie von der MinGW-Shell aus GTK+
+      und weitere Entwicklungswerkzeuge:
+      \begin{lstlisting}[style=cmd,gobble=8]
+        pacman -S mingw-w64-x86_64-gcc
+        pacman -S mingw-w64-x86_64-gtk3
+        pacman -S mingw-w64-x86_64-pkg-config
+      \end{lstlisting}
+    \item
+      Falls nötig, ergänzen Sie in der MinGW-Shell
+      den Pfad zu den neu installierten Programmen:
+      \begin{lstlisting}[style=cmd,gobble=8]
+        export PATH=$PATH:/mingw64/bin
+      \end{lstlisting}
+  \end{itemize}
+
+  \bigskip
+
+  \strut\hfill\emph{Viel Erfolg!}
+
+  \vfill
+
+  \begingroup
+
+    \small
+
+    \setlength{\leftskip}{3cm}
+
+    Stand: 9.\ Januar 2020
+
+%    Soweit nicht anders angegeben:\\
+    Copyright \copyright\ 2014, 2015, 2016, 2018, 2019, 2020\quad Peter Gerwinski\\
+    Lizenz: \mylicense
+
+    Sie können diese Praktikumsunterlagen einschließlich Quelltext
+%    und Beispielprogramme\\
+    herunterladen unter:\\
+    \url{https://gitlab.cvh-server.de/pgerwinski/hp}
+
+  \endgroup
+
+\end{document}
diff --git a/20200109/hp-20200109.pdf b/20200109/hp-20200109.pdf
new file mode 100644
index 0000000000000000000000000000000000000000..f85a40fc9c6567ec45374e947082fd739d37d011
Binary files /dev/null and b/20200109/hp-20200109.pdf differ
diff --git a/20200109/hp-20200109.tex b/20200109/hp-20200109.tex
new file mode 100644
index 0000000000000000000000000000000000000000..999bf9ef028b1041627dc22860e41e1e6b5f74f4
--- /dev/null
+++ b/20200109/hp-20200109.tex
@@ -0,0 +1,1265 @@
+% hp-20200109.pdf - Lecture Slides on Low-Level Programming
+% Copyright (C) 2012, 2013, 2015, 2016, 2017, 2018, 2019, 2020  Peter Gerwinski
+%
+% This document is free software: you can redistribute it and/or
+% modify it either under the terms of the Creative Commons
+% Attribution-ShareAlike 3.0 License, or under the terms of the
+% GNU General Public License as published by the Free Software
+% Foundation, either version 3 of the License, or (at your option)
+% any later version.
+%
+% This document is distributed in the hope that it will be useful,
+% but WITHOUT ANY WARRANTY; without even the implied warranty of
+% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+% GNU General Public License for more details.
+%
+% You should have received a copy of the GNU General Public License
+% along with this document.  If not, see <http://www.gnu.org/licenses/>.
+%
+% You should have received a copy of the Creative Commons
+% Attribution-ShareAlike 3.0 Unported License along with this
+% document.  If not, see <http://creativecommons.org/licenses/>.
+
+% README: Rekursion, Aufwandsabschätzungen, objektorientierte Programmierung
+
+\documentclass[10pt,t]{beamer}
+
+\usepackage{pgslides}
+\usepackage{tikz}
+\usepackage{rotating}
+
+\usefonttheme[onlymath]{serif}
+
+\definecolor{medcyan}{rgb}{0.0,0.5,0.7}
+
+\title{Hardwarenahe Programmierung}
+\author{Prof.\ Dr.\ rer.\ nat.\ Peter Gerwinski}
+\date{9.\ Januar 2020}
+
+\begin{document}
+
+\maketitleframe
+
+\nosectionnonumber{\inserttitle}
+
+\begin{frame}
+
+  \shownosectionnonumber
+
+  \begin{itemize}
+    \item[\textbf{1}] \textbf{Einführung}
+      \hfill\makebox(0,0)[br]{\raisebox{2.25ex}{\url{https://gitlab.cvh-server.de/pgerwinski/hp}}}
+    \item[\textbf{2}] \textbf{Einführung in C}
+    \item[\textbf{3}] \textbf{Bibliotheken}
+    \item[\textbf{4}] \textbf{Hardwarenahe Programmierung}
+      \begin{itemize}
+        \vspace*{-0.1cm}
+        \item[\dots]
+%        \item[4.3] Interrupts
+        \item[4.4] volatile-Variable
+        \item[4.6] Byte-Reihenfolge -- Endianness
+        \color{medgreen}
+        \item[4.7] Binärdarstellung negativer Zahlen
+        \item[4.8] Speicherausrichtung -- Alignment
+      \end{itemize}
+    \item[\textbf{5}] \textbf{Algorithmen}
+      \begin{itemize}
+        \item[5.1] Differentialgleichungen
+        \color{medcyan}
+        \item[5.\hbox to 0.56em{\boldmath$\frac{1+i}{\sqrt2}$}]\hspace*{0.90em}Quantencomputer
+        \vspace*{1pt}
+        \color{red}
+        \item[5.2] Rekursion
+        \item[5.3] Aufwandsabschätzungen
+%        \vspace*{-0.1cm}
+        \item[\dots]
+      \end{itemize}
+    \vspace*{-\smallskipamount}
+    \item[\textbf{\dots}]
+  \end{itemize}
+
+\end{frame}
+
+\setcounter{section}{3}
+\section{Hardwarenahe Programmierung}
+\setcounter{subsection}{5}
+\subsection{Byte-Reihenfolge -- Endianness}
+\subsubsection{Konzept}
+
+\begin{frame}[fragile]
+
+  \showsubsection
+  \showsubsubsection
+
+  Eine Zahl geht über mehrere Speicherzellen.\\
+  Beispiel: 16-Bit-Zahl in 2 8-Bit-Speicherzellen
+
+  \smallskip
+
+  Welche Bits liegen wo?
+
+%  \pause
+  \bigskip
+
+  $1027 = 1024 + 2 + 1 = 0000\,0100\,0000\,0011_2 = 0403_{16}$
+
+%  \pause
+  \bigskip
+  Speicherzellen:
+
+  \medskip
+  \begin{tabular}{|c|c|l}\cline{1-2}
+    \raisebox{-0.25ex}{04} & \raisebox{-0.25ex}{03} & \strut Big-Endian "`großes Ende zuerst"' \\\cline{1-2}
+    \multicolumn{2}{c}{} & für Menschen leichter lesbar \\
+    \multicolumn{3}{c}{} \\[-5pt]\cline{1-2}
+    \raisebox{-0.25ex}{03} & \raisebox{-0.25ex}{04} & \strut Little-Endian "`kleines Ende zuerst"' \\\cline{1-2}
+    \multicolumn{2}{c}{} & bei Additionen effizienter
+  \end{tabular}
+
+%  \pause
+  \medskip
+  \textarrow\ Geschmackssache
+%  \pause\\
+  \quad\textbf{\dots\ außer bei Datenaustausch!}
+
+%  \pause
+%  \bigskip
+%
+%  Aber: nicht verwechseln! \qquad $0304_{16} = 772$
+
+\end{frame}
+
+\iffalse
+
+\begin{frame}
+
+  \showsubsection
+  \showsubsubsection
+
+  Eine Zahl geht über mehrere Speicherzellen.\\
+  Beispiel: 16-Bit-Zahl in 2 8-Bit-Speicherzellen
+
+  \smallskip
+
+  Welche Bits liegen wo?
+
+  \medskip
+
+  \textarrow\ Geschmackssache\\
+  \textbf{\dots\ außer bei Datenaustausch!}
+
+  \begin{itemize}
+    \item
+      Dateiformate
+    \item
+      Datenübertragung
+  \end{itemize}
+
+\end{frame}
+
+\subsubsection{Dateiformate}
+
+\begin{frame}
+
+  \showsubsection
+  \showsubsubsection
+
+  Audio-Formate: Reihenfolge der Bytes in 16- und 32-Bit-Zahlen
+  \begin{itemize}
+    \item
+      RIFF-WAVE-Dateien (\file{.wav}): Little-Endian
+    \item
+      Au-Dateien (\file{.au}): Big-Endian
+%    \pause
+    \item
+      ältere AIFF-Dateien (\file{.aiff}): Big-Endian
+    \item
+      neuere AIFF-Dateien (\file{.aiff}): Little-Endian
+  \end{itemize}
+
+%  \pause
+  \bigskip
+
+  Grafik-Formate: Reihenfolge der Bits in den Bytes
+  \begin{itemize}
+    \item
+      PBM-Dateien: Big-Endian\only<1->{, MSB first}
+    \item
+      XBM-Dateien: Little-Endian\only<1->{, LSB first}
+  \end{itemize}
+  \only<1->{MSB/LSB = most/least significant bit}
+
+\end{frame}
+
+\subsubsection{Datenübertragung}
+
+\begin{frame}
+
+  \showsubsection
+  \showsubsubsection
+
+  \begin{itemize}
+    \item
+      RS-232 (serielle Schnittstelle): LSB first
+    \item
+      I$^2$C: MSB first
+    \item
+      USB: beides
+%    \pause
+    \medskip
+    \item
+      Ethernet: LSB first
+    \item
+      TCP/IP (Internet): Big-Endian
+  \end{itemize}
+
+\end{frame}
+
+\fi
+
+\subsection{Binärdarstellung negativer Zahlen}
+
+\begin{frame}[fragile]
+
+  \showsubsection
+
+  Speicher ist begrenzt!\\
+  \textarrow\ feste Anzahl von Bits
+
+  \medskip
+
+  8-Bit-Zahlen ohne Vorzeichen: \lstinline{uint8_t}\\
+  \textarrow\ Zahlenwerte von \lstinline{0x00} bis \lstinline{0xff} = 0 bis 255\\
+%  \pause
+  \textarrow\ 255 + 1 = 0
+
+%  \pause
+  \medskip
+
+  8-Bit-Zahlen mit Vorzeichen: \lstinline{int8_t}\\
+  \lstinline{0xff} = 255 ist die "`natürliche"' Schreibweise für $-1$.\\
+%  \pause
+  \textarrow\ Zweierkomplement
+
+%  \pause
+  \medskip
+
+  Oberstes Bit = 1: negativ\\
+  Oberstes Bit = 0: positiv\\
+  \textarrow\ 127 + 1 = $-128$
+
+\end{frame}
+
+\begin{frame}[fragile]
+
+  \showsubsection
+
+  Speicher ist begrenzt!\\
+  \textarrow\ feste Anzahl von Bits
+
+  \medskip
+
+  16-Bit-Zahlen ohne Vorzeichen:
+  \lstinline{uint16_t}\hfill\lstinline{uint8_t}\\
+  \textarrow\ Zahlenwerte von \lstinline{0x0000} bis \lstinline{0xffff}
+  = 0 bis 65535\hfill 0 bis 255\\
+  \textarrow\ 65535 + 1 = 0\hfill 255 + 1 = 0
+
+  \medskip
+
+  16-Bit-Zahlen mit Vorzeichen:
+  \lstinline{int16_t}\hfill\lstinline{int8_t}\\
+  \lstinline{0xffff} = 66535 ist die "`natürliche"' Schreibweise für $-1$.\hfill
+  \lstinline{0xff} = 255 = $-1$\\
+  \textarrow\ Zweierkomplement
+
+  \medskip
+
+  Oberstes Bit = 1: negativ\\
+  Oberstes Bit = 0: positiv\\
+  \textarrow\ 32767 + 1 = $-32768$
+
+  \bigskip
+  Literatur: \url{http://xkcd.com/571/}
+
+\end{frame}
+
+\begin{frame}[fragile]
+
+  \showsubsection
+
+  Frage: \emph{Für welche Zahl steht der Speicherinhalt\,
+  \raisebox{2pt}{%
+    \tabcolsep0.25em
+    \begin{tabular}{|c|c|}\hline
+      \rule{0pt}{11pt}a3 & 90 \\\hline
+    \end{tabular}}
+  (hexadezimal)?}
+  
+%  \pause
+  \smallskip
+  Antwort: \emph{Das kommt darauf an.} ;--)
+
+%  \pause
+  \medskip
+  Little-Endian:
+
+  \smallskip
+
+  \begin{tabular}{lrl}
+    als \lstinline,int8_t,: & $-93$ & (nur erstes Byte)\\
+    als \lstinline,uint8_t,: & $163$ & (nur erstes Byte)\\
+    als \lstinline,int16_t,: & $-28509$\\
+    als \lstinline,uint16_t,: & $37027$\\
+    \lstinline,int32_t, oder größer: & $37027$
+      & (zusätzliche Bytes mit Nullen aufgefüllt)
+  \end{tabular}
+
+%  \pause
+  \medskip
+  Big-Endian:
+
+  \smallskip
+
+  \begin{tabular}{lrl}
+    als \lstinline,int8_t,:   & $-93$ & (nur erstes Byte)\\
+    als \lstinline,uint8_t,:  & $163$ & (nur erstes Byte)\\
+    als \lstinline,int16_t,:  & $-23664$\\
+    als \lstinline,uint16_t,: & $41872$\\
+    als \lstinline,int32_t,:  & $-1550843904$ & (zusätzliche Bytes\\
+    als \lstinline,uint32_t,: & $2744123392$  & mit Nullen aufgefüllt)\\
+    als \lstinline,int64_t,:  & $-6660823848880963584$\\
+    als \lstinline,uint64_t,: & $11785920224828588032$\\
+  \end{tabular}
+
+  \vspace*{-1cm}
+
+\end{frame}
+
+\subsection{Speicherausrichtung -- Alignment}
+
+\begin{frame}[fragile]
+
+  \showsubsection
+
+  \begin{lstlisting}
+    #include <stdint.h>
+
+    uint8_t a;
+    uint16_t b;
+    uint8_t c;
+  \end{lstlisting}
+
+%  \pause
+  \bigskip
+
+  Speicheradresse durch 2 teilbar -- "`16-Bit-Alignment"'
+  \begin{itemize}
+    \item
+      2-Byte-Operation: effizienter
+%    \pause
+    \item
+      \dots\ oder sogar nur dann erlaubt
+%    \pause
+    \arrowitem
+      Compiler optimiert Speicherausrichtung
+  \end{itemize}
+
+  \medskip
+
+%  \pause
+  \begin{minipage}{3cm}
+    \begin{lstlisting}[gobble=6]
+      ¡uint8_t a;
+      uint8_t dummy;
+      uint16_t b;
+      uint8_t c;¿
+    \end{lstlisting}
+  \end{minipage}
+%  \pause
+  \begin{minipage}{3cm}
+    \begin{lstlisting}[gobble=6]
+      ¡uint8_t a;
+      uint8_t c;
+      uint16_t b;¿
+    \end{lstlisting}
+  \end{minipage}
+
+%  \pause
+  \vspace{-1.75cm}
+  \strut\hfill
+  \begin{minipage}{6.5cm}
+    Fazit:
+    \begin{itemize}
+      \item
+        \textbf{Adressen von Variablen\\
+        sind systemabhängig}
+      \item
+        Bei Definition von Datenformaten\\
+        Alignment beachten \textarrow\ effizienter
+    \end{itemize}
+  \end{minipage}
+
+\end{frame}
+
+\section{Algorithmen}
+\setcounter{subsection}{1}
+\subsection{Rekursion}
+
+\begin{frame}[fragile]
+
+  \showsubsection
+
+  Vollständige Induktion:
+  \vspace*{-0.725cm}
+  \begin{displaymath}
+    \hspace*{4cm}
+    \left.
+      \begin{array}{r}
+        \mbox{Aussage gilt für $n = 1$}\\[2pt]
+        \mbox{Schluß von $n - 1$ auf $n$}
+      \end{array}
+    \right\}
+    \mbox{Aussage gilt für alle $n\in\mathbb{N}$}
+  \end{displaymath}
+  \vspace*{-0.5cm}
+
+  \pause
+
+  Türme von Hanoi
+
+  \begin{onlyenv}<2>
+    \begin{center}
+      \includegraphics[width=12.2cm]{Tower_of_Hanoi.jpeg}
+    \end{center}
+  \end{onlyenv}
+
+  \begin{onlyenv}<3->
+    \begin{itemize}
+      \item
+        64 Scheiben, 3 Plätze,
+        \only<3-4>{\hfill\makebox(0,0)[rt]{\includegraphics[width=6cm]{Tower_of_Hanoi.jpeg}}}\\
+        immer 1 Scheibe verschieben
+      \item
+        Ziel: Turm verschieben
+      \item
+        Es dürfen nur kleinere Scheiben\\
+        auf größeren liegen.
+      \bigskip
+      \pause
+      \pause
+      \item
+        $n = 1$ Scheibe: fertig
+      \item
+        Wenn $n - 1$ Scheiben verschiebbar:\\
+        schiebe $n - 1$ Scheiben auf Hilfsplatz,\\
+        verschiebe die darunterliegende,\\
+        hole $n - 1$ Scheiben von Hilfsplatz
+    \end{itemize}
+    \begin{onlyenv}<5>
+      \vspace{-4.3cm}
+      \begin{lstlisting}[gobble=8,xleftmargin=6.4cm]
+        void move (int from, int to, int disks)
+        {
+          if (disks == 1)
+            move_one_disk (from, to);
+          else
+            {
+              int help = 0 + 1 + 2 - from - to;
+              move (from, help, disks - 1);
+              move (from, to, 1);
+              move (help, to, disks - 1);
+            }
+        }
+      \end{lstlisting}
+    \end{onlyenv}
+    \begin{onlyenv}<6->
+      \vspace{-5.0cm}
+      \hspace*{7.4cm}\begin{minipage}[t]{5cm}
+        32 Scheiben:
+        \begin{lstlisting}[gobble=10,style=terminal]
+          $ ¡time ./hanoi-9a¿
+          ...
+          real    0m32,712s
+          user    0m32,708s
+          sys     0m0,000s
+        \end{lstlisting}
+        \pause[7]
+        \begin{itemize}
+          \arrowitem
+            etwas über 1 Minute\\
+            für 64 Scheiben
+        \end{itemize}
+        \pause
+        \vspace*{-0.5cm}
+        \begin{picture}(0,0)
+          \color{red}
+          \put(0,0){\makebox(0,0)[bl]{\tikz[line width=1pt]{\draw(0,0)--(4,0.8);}}}
+          \put(0,0.8){\makebox(0,0)[tl]{\tikz[line width=1pt]{\draw(0,0)--(4,-0.8);}}}
+        \end{picture}
+
+        Für jede zusätzliche Scheibe\\verdoppelt sich die Rechenzeit!
+        % 32.712 * 2^32 / 3600 / 24 / 365.25 = 4452.08032888280477602859
+        \begin{itemize}
+          \arrowitem
+            $\frac{32,712\,\text{s}\,\cdot\,2^{32}}{3600\,\cdot\,24\,\cdot\,365,25} \approx 4452$
+            Jahre\\[\smallskipamount]
+            für 64 Scheiben
+        \end{itemize}
+      \end{minipage}
+    \end{onlyenv}
+  \end{onlyenv}
+
+\end{frame}
+
+\subsection{Aufwandsabschätzungen \protect\color{gray}-- Komplexitätsanalyse}
+
+\begin{frame}[fragile]
+
+%  \newcommand{\w}{\hspace*{0.75pt}}
+
+  \showsubsection
+
+  \begin{picture}(0,0)
+    \put(7.6,-0.5){%
+      \begin{minipage}[t]{5.3cm}
+%        \vspace*{-1.0cm}\includegraphics{landau-symbols.pdf}
+        \vspace*{-1.0cm}\alt<6->{\includegraphics{landau-symbols-3.pdf}}%
+                       {\alt<5->{\includegraphics{landau-symbols-2.pdf}}%
+                                {\includegraphics{landau-symbols.pdf}}}
+        \small
+        \begin{description}\itemsep0pt\leftskip-0.5cm
+          \item[$n$:] Eingabedaten
+          \item[$g(n)$:] Rechenzeit
+        \end{description}
+      \end{minipage}}
+  \end{picture}
+
+  \vspace*{-\bigskipamount}
+
+  Wann ist ein Programm "`schnell"'?
+
+  \medskip
+
+  \begin{onlyenv}<1-2>
+      Türme von Hanoi: $\mathcal{O}(2^n)$
+      \par\medskip
+      Für jede zusätzliche Scheibe\\verdoppelt sich die Rechenzeit!
+      % 32.712 * 2^32 / 3600 / 24 / 365.25 = 4452.08032888280477602859
+      \begin{itemize}
+        \arrowitem
+          $\frac{32,712\,\text{s}\,\cdot\,2^{32}}{3600\,\cdot\,24\,\cdot\,365,25} \approx 4452$
+          Jahre\\[\smallskipamount]
+          für 64 Scheiben
+      \end{itemize}
+
+      \bigskip
+  \end{onlyenv}
+
+  \begin{onlyenv}<2->
+    Faustregel:\\Schachtelung der Schleifen zählen\\
+    $k$ Schleifen ineinander \textarrow\ $\mathcal{O}(n^k)$
+
+    \bigskip
+  \end{onlyenv}
+
+  \begin{onlyenv}<3>
+    \textbf{Beispiel: Sortieralgorithmen}
+
+    \smallskip
+
+    Anzahl der Vergleiche bei $n$ Strings
+    \begin{itemize}
+      \item
+        Maximum suchen mit Schummeln: $\mathcal{O}(1)$
+      \item
+        Maximum suchen: $\mathcal{O}(n)$
+      \item
+        Selection-Sort: $\mathcal{O}(n^2)$
+      \item
+        Bubble-Sort: $\mathcal{O}(n)$ bis $\mathcal{O}(n^2)$
+      \item
+        Quicksort: $\mathcal{O}(n\log n)$ bis $\mathcal{O}(n^2)$
+    \end{itemize}
+
+  \end{onlyenv}
+
+  \begin{onlyenv}<4>
+    \textbf{Wie schnell ist RSA-Verschlüsselung?}
+
+    \smallskip
+
+    \begin{math}
+      c = m^e\,\%\,N
+    \end{math}
+    \quad
+    ("`$\%$"' = "`modulo"')
+
+    \medskip
+
+    \begin{lstlisting}[gobble=6,xleftmargin=2em]
+      int c = 1;
+      for (int i = 0; i < e; i++)
+        c = (c * m) % N;
+    \end{lstlisting}
+
+    \smallskip
+
+    \begin{itemize}
+      \item
+        $\mathcal{O}(e)$ Iterationen
+%      \item
+%        wenn $n$ die Anzahl der Binärziffern (Bits) von $e$ ist:
+%        $\mathcal{O}(2^n)$ Iterationen
+      \item
+        mit Trick:
+        $\mathcal{O}(\log e)$ Iterationen ($\log e$ = Anzahl der Ziffern von $e$)
+    \end{itemize}
+
+    \smallskip
+
+    Jede Iteration enthält eine Multiplikation und eine Division.\\
+    Aufwand dafür: $\mathcal{O}(\log e)$\\
+    \textarrow\ Gesamtaufwand: $\mathcal{O}\bigl((\log e)^2\bigr)$
+
+  \end{onlyenv}
+
+  \begin{onlyenv}<5->
+
+    \textbf{Wie schnell ist RSA?}\\
+
+    \smallskip
+
+    ($n$ = typische beteiligte Zahl, z.\,B. $e,p,q$)
+
+    \begin{itemize}
+      \item
+        Ver- und Entschlüsselung (Exponentiation):\\
+        \strut\hbox to 3.5cm{\color{red}$\mathcal{O}\!\left((\log n)^2\right)$\hss}
+        \only<6->{{\color{magenta}$\mathcal{O}(n^2)$}}
+      \item
+        Schlüsselerzeugung (Berechnung von $d$):\\
+        \strut\hbox to 3.5cm{\color{red}$\mathcal{O}\!\left((\log n)^2\right)$\hss}
+        \only<6->{{\color{magenta}$\mathcal{O}(n^2)$}}
+      \item
+        Verschlüsselung brechen (Primfaktorzerlegung):\\
+        \strut\hbox to 3.5cm{\color{red}$\mathcal{O}\bigl(2^{\sqrt{\log n\,\cdot\,\log\log n}}\bigr)$\hss}
+        \only<6->{{\color{magenta}$\mathcal{O}\bigl(2^{\sqrt{n\log n}}\bigr)$}}
+    \end{itemize}
+
+    \vspace{0cm plus 1filll}
+
+    \textbf{Die Sicherheit von RSA beruht darauf,
+    daß das Brechen der Verschlüsselung aufwendiger ist als
+    \boldmath$\mathcal{O}\bigl((\log n)^k\bigr)$ (für beliebiges $k$).}
+
+    \vspace*{0.65cm}
+
+  \end{onlyenv}
+
+\end{frame}
+
+\section{Objektorientierte Programmierung}
+
+\iffalse
+
+\addtocounter{subsection}{-1}
+\subsection{Dynamische Speicherverwaltung}
+
+\begin{frame}[fragile]
+
+  \showsection
+  \showsubsection
+
+  \begin{itemize}
+    \item
+      Array: feste Anzahl von Elementen desselben Typs (z.\,B.\ 3 ganze Zahlen)
+    \item
+      Dynamisches Array: variable Anzahl von Elementen desselben Typs
+  \end{itemize}
+
+  \bigskip
+
+  \begin{lstlisting}
+    char *name[] = { "Anna", "Berthold", "Caesar" };
+
+    ...
+
+     name[3] = "Dieter";
+  \end{lstlisting}
+
+  \begin{picture}(0,0)
+    \color{red}
+    \put(0,0){\line(3,1){3.5}}
+    \put(0,1){\line(3,-1){3.5}}
+  \end{picture}
+
+\end{frame}
+
+\begin{frame}[fragile]
+
+  \showsection
+  \showsubsection
+
+  \bigskip
+
+  \begin{lstlisting}
+    #include <stdlib.h>
+
+    ...
+
+      char **name = malloc (3 * sizeof (char *));
+        /* Speicherplatz für 3 Zeiger anfordern */
+
+    ...
+
+      free (name)
+        /* Speicherplatz freigeben */
+
+  \end{lstlisting}
+
+\end{frame}
+
+\fi
+
+\subsection{Konzepte und Ziele}
+
+\begin{frame}
+
+  \showsection
+  \showsubsection
+
+  \begin{itemize}
+    \item
+%      Array: feste Anzahl von Elementen desselben Typs (z.\,B.\ 3 ganze Zahlen)
+      Array: Elemente desselben Typs (z.\,B.\ 3 ganze Zahlen)
+%    \item
+%      Dynamisches Array: variable Anzahl von Elementen desselben Typs
+    \item
+      Problem: Elemente unterschiedlichen Typs
+    \item
+      Lösung: den Typ des Elements zusätzlich speichern
+  \end{itemize}
+  \begin{itemize}
+    \item
+      Funktionen, die mit dem Objekt arbeiten: \newterm{Methoden}
+    \begin{onlyenv}<1>
+      \item
+        Was die Funktion bewirkt,\\
+        hängt vom Typ des Objekts ab
+      \item
+        Realisierung über endlose \lstinline{if}-Ketten
+    \end{onlyenv}
+    \begin{onlyenv}<2>
+      \item
+        Was die Funktion bewirkt
+        \begin{picture}(0,0)
+          \color{red}
+          \put(-4.00,-0.10){\tikz{\draw[thick](0,0.25)--(3.75,-0.05);%
+                                  \draw[thick](-0.1,-0.05)--(3.75,0.3);}}
+        \end{picture}%
+        Welche Funktion aufgerufen wird,\\
+        hängt vom Typ des Objekts ab: \newterm{virtuelle Methode}
+      \item
+        Realisierung über endlose \lstinline{if}-Ketten%
+        \begin{picture}(0,0)
+          \color{red}
+          \put(-2.75,-0.10){\tikz{\draw[thick](0,0.25)--(2.5,-0.05);%
+                                  \draw[thick](-0.1,-0.05)--(2.5,0.3);}}
+          \put(1.5,-1.1){\begin{rotate}{7}\large\bf\textarrow\
+%                           kommt gleich
+                           nächste Woche
+                         \end{rotate}}
+        \end{picture}
+        Zeiger, die im Objekt gespeichert sind\\
+        (Genaugenommen: Tabelle von Zeigern)
+    \end{onlyenv}
+  \end{itemize}
+
+\end{frame}
+
+\begin{frame}
+
+  \showsection
+  \showsubsection
+
+  \begin{itemize}
+    \item
+      Problem: Elemente unterschiedlichen Typs
+    \item
+      Lösung: den Typ des Elements zusätzlich speichern
+    \item
+      \newterm{Methoden\/} und \newterm{virtuelle Methoden}
+  \end{itemize}
+
+  \begin{itemize}
+    \item
+      Zeiger auf verschiedene Strukturen\\
+      mit einem gemeinsamen Anteil von Datenfeldern\\
+      \textarrow\ "`verwandte"' \newterm{Objekte}, \newterm{Klassen} von Objekten
+    \item
+      Struktur, die \emph{nur\/} den gemeinsamen Anteil enthält\\
+      \textarrow\ "`Vorfahr"', \newterm{Basisklasse}, \newterm{Vererbung}
+    \item
+%      Explizite Typumwandlung eines Zeigers auf die Basisklasse\\
+%      in einen Zeiger auf die \newterm{abgeleitete Klasse}\\
+%      \textarrow\ Man kann ein Array unterschiedlicher Objekte\\
+%      \strut\phantom{\textarrow} in einer Schleife abarbeiten.\\
+      Zeiger auf die Basisklasse dürfen auf Objekte\\
+      der \newterm{abgeleiteten Klasse} zeigen\\
+      \textarrow\ \newterm{Polymorphie}
+  \end{itemize}
+
+\end{frame}
+
+\subsection{Beispiel: Zahlen und Buchstaben}
+
+\begin{frame}[fragile]
+
+  \showsection
+  \showsubsection
+
+  \begin{center}
+    \begin{minipage}{5cm}
+      \begin{lstlisting}[gobble=8]
+        ¡typedef struct
+        {
+          int type;
+        } t_base;¿
+      \end{lstlisting}
+    \end{minipage}\\[0.5cm]
+    \begin{minipage}{5cm}
+      \begin{lstlisting}[gobble=8]
+        ¡typedef struct
+        {
+          int type;
+          int content;
+        } t_integer;¿
+      \end{lstlisting}
+    \end{minipage}
+    \begin{minipage}{5cm}
+      \begin{lstlisting}[gobble=8]
+        ¡typedef struct
+        {
+          int type;
+          char *content;
+        } t_string;¿
+      \end{lstlisting}
+    \end{minipage}
+  \end{center}
+  
+\end{frame}
+
+\begin{frame}[fragile]
+  \begin{center}
+    \begin{minipage}{5cm}
+      \begin{lstlisting}[gobble=8]
+        ¡typedef struct
+        {
+          int type;
+        } t_base;¿
+      \end{lstlisting}
+    \end{minipage}\\[0.5cm]
+    \begin{minipage}{5cm}
+      \begin{lstlisting}[gobble=8]
+        ¡typedef struct
+        {
+          int type;
+          int content;
+        } t_integer;¿
+      \end{lstlisting}
+    \end{minipage}
+    \begin{minipage}{5cm}
+      \begin{lstlisting}[gobble=8]
+        ¡typedef struct
+        {
+          int type;
+          char *content;
+        } t_string;¿
+      \end{lstlisting}
+    \end{minipage}\\[0.7cm]
+    \begin{onlyenv}<1>
+      \begin{minipage}{8cm}
+        \begin{lstlisting}[gobble=10]
+          ¡t_integer i = { 1, 42 };
+          t_string s = { 2, "Hello, world!" };
+
+          t_base *object[] = { (t_base *) &i, (t_base *) &s };¿
+        \end{lstlisting}
+      \end{minipage}%
+      \begin{picture}(0,0)
+        \color{red}
+        \put(-5.4,-0.8){\mbox{$\underbrace{\rule{1.45cm}{0pt}}_{\shortstack{\strut explizite\\Typumwandlung}}$}}
+      \end{picture}
+    \end{onlyenv}
+%    \begin{onlyenv}<2>
+%      \begin{minipage}{5cm}
+%        \begin{lstlisting}[gobble=10]
+%          ¡typedef union
+%          {
+%            t_base base;
+%            t_integer integer;
+%            t_string string;
+%          } t_object;¿
+%        \end{lstlisting}
+%      \end{minipage}
+%    \end{onlyenv}
+  \end{center}
+  
+\end{frame}
+
+\iffalse
+
+\subsection{Unions}
+
+\begin{frame}[fragile]
+
+  \showsubsection
+
+  Variable teilen sich denselben Speicherplatz.
+
+  \medskip
+
+  \begin{minipage}[t]{3.7cm}
+    \begin{lstlisting}[gobble=6]
+      ¡typedef union
+      {
+        int8_t i;
+        uint8_t u;
+      } num8_t;¿
+    \end{lstlisting}
+  \end{minipage}%
+  \begin{minipage}[t]{4.5cm}
+    \begin{lstlisting}[gobble=6]
+      ¡int main (void)
+      {
+        num8_t test;
+        test.i = -1;
+        printf ("%d\n", test.u);
+        return 0;
+      }¿
+    \end{lstlisting}
+  \end{minipage}
+
+\end{frame}
+
+\begin{frame}[fragile]
+
+  \showsubsection
+
+  Variable teilen sich denselben Speicherplatz.
+
+  \medskip
+
+  \begin{minipage}[t]{3.7cm}
+    \begin{lstlisting}[gobble=6]
+      ¡typedef union
+      {
+        char s[8];
+        uint64_t x;
+      } num_char_t;¿
+    \end{lstlisting}
+  \end{minipage}%
+  \begin{minipage}[t]{4.5cm}
+    \begin{lstlisting}[gobble=6]
+      ¡int main (void)
+      {
+        num_char_t test = { "Hello!" };
+        printf ("%lx\n", test.x);
+        return 0;
+      }¿
+    \end{lstlisting}
+  \end{minipage}
+
+\end{frame}
+
+\begin{frame}[fragile]
+
+  \showsubsection
+
+  Variable teilen sich denselben Speicherplatz.
+
+  \medskip
+
+  \begin{minipage}[t]{3.7cm}
+    \begin{lstlisting}[gobble=6]
+      ¡typedef union
+      {
+        t_base base;
+        t_integer integer;
+        t_string string;
+      } t_object;¿
+    \end{lstlisting}
+  \end{minipage}%
+  \begin{minipage}[t]{3.0cm}
+    \begin{lstlisting}[gobble=6]
+
+      ¡typedef struct
+      {
+        int type;
+      } t_base;¿
+    \end{lstlisting}
+  \end{minipage}%
+  \begin{minipage}[t]{3.0cm}
+    \begin{lstlisting}[gobble=6]
+
+      ¡typedef struct
+      {
+        int type;
+        int content;
+      } t_integer;¿
+    \end{lstlisting}
+  \end{minipage}%
+  \begin{minipage}[t]{3.0cm}
+    \begin{lstlisting}[gobble=6]
+
+      ¡typedef struct
+      {
+        int type;
+        char *content;
+      } t_string;¿
+    \end{lstlisting}
+  \end{minipage}
+
+  \bigskip
+
+  \begin{center}
+    \begin{minipage}{8.5cm}
+      \begin{lstlisting}[gobble=8]
+        ¡if (this->base.type == T_INTEGER)
+          printf ("Integer: %d\n", this->integer.content);
+        else if (this->base.type == T_STRING)
+          printf ("String: \"%s\"\n", this->string.content);¿
+      \end{lstlisting}
+    \end{minipage}
+  \end{center}
+
+\end{frame}
+
+\subsection{Virtuelle Methoden}
+
+\begin{frame}[fragile]
+  \showsubsection
+
+  \begin{lstlisting}
+    void print_object (t_object *this)
+    {
+      if (this->base.type == T_INTEGER)
+        printf ("Integer: %d\n", this->integer.content);
+      else if (this->base.type == T_STRING)
+        printf ("String: \"%s\"\n", this->string.content);
+    }
+  \end{lstlisting}
+
+  \begin{picture}(0,0)
+    \color{red}
+    \put(9,1.7){\shortstack[l]{if-Kette:\\\strut wird unübersichtlich}}
+    \put(1,-2){\mbox{\textarrow}}
+    \put(0,-3){\mbox{Zeiger auf Funktionen}}
+  \end{picture}
+
+  \begin{lstlisting}[xleftmargin=4cm]
+    void print_integer (t_object *this)
+    {
+      printf ("Integer: %d\n", this->integer.content);
+    }
+
+    void print_string (t_object *this)
+    {
+      printf ("String: \"%s\"\n", this->string.content);
+    }
+  \end{lstlisting}
+
+\end{frame}
+
+\begin{frame}[fragile]
+  \showsubsection
+
+  Zeiger auf Funktionen
+
+  \medskip
+
+  \begin{lstlisting}
+    void (* print) (t_object *this);
+  \end{lstlisting}
+  \begin{picture}(0,1.2)(0,-0.9)
+    \color{red}
+    \put(0.95,0.3){\mbox{$\underbrace{\rule{1cm}{0pt}}$}}
+    \put(0.2,-0.7){\shortstack{das, worauf print zeigt,\\ist eine Funktion}}
+  \end{picture}
+
+  \begin{itemize}
+    \item
+      Objekt enthält Zeiger auf Funktion
+      \begin{onlyenv}<1>
+        \medskip
+        \begin{lstlisting}[gobble=10]
+          typedef struct
+          {
+            void (* print) (union t_object *this);
+            int content;
+          } t_integer;
+        \end{lstlisting}
+      \end{onlyenv}
+      \begin{onlyenv}<2->
+        \vspace*{-3.5cm}  % Why doesn't a picture environment work here??? :-(
+        \begin{lstlisting}[gobble=10,xleftmargin=5.5cm]
+          typedef struct
+          {
+            void (* print) (union t_object *this);
+            int content;
+          } t_integer;
+        \end{lstlisting}
+        \vspace*{0.85cm}
+        \bigskip
+        \smallskip
+      \end{onlyenv}
+    \pause
+    \item
+      Konstruktor initialisiert diesen Zeiger
+      \begin{onlyenv}<2>
+        \medskip
+        \begin{lstlisting}[gobble=10]
+          t_object *new_integer (int i)
+          {
+            t_object *p = malloc (sizeof (t_integer));
+            p->integer.print = print_integer;
+            p->integer.content = i;
+            return p;
+          }
+        \end{lstlisting}
+        \vspace*{-2cm}
+      \end{onlyenv}
+    \pause
+    \item
+      Aufruf: "`automatisch"' die richtige Funktion
+      \begin{onlyenv}<3>
+        \medskip
+        \begin{lstlisting}[gobble=10]
+          for (int i = 0; object[i]; i++)
+            object[i]->base.print (object[i]);
+        \end{lstlisting}
+      \end{onlyenv}
+    \pause
+    \medskip
+    \item
+      in größeren Projekten:\\
+      Objekt enthält Zeiger auf Tabelle von Funktionen
+  \end{itemize}
+\end{frame}
+
+\subsection{Beispiel: Graphische Benutzeroberfläche (GUI)}
+
+\begin{frame}[fragile]
+
+  \showsubsection
+
+  \scriptsize
+  \begin{lstlisting}
+    #include <gtk/gtk.h>
+
+    int main (int argc, char **argv)
+    {
+      gtk_init (&argc, &argv);
+      GtkWidget *window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+      gtk_window_set_title (GTK_WINDOW (window), "Hello");
+      g_signal_connect (window, "destroy", G_CALLBACK (gtk_main_quit), NULL);
+      GtkWidget *vbox = gtk_box_new (GTK_ORIENTATION_VERTICAL, 5);
+      gtk_container_add (GTK_CONTAINER (window), vbox);
+      gtk_container_set_border_width (GTK_CONTAINER (vbox), 10);
+      GtkWidget *label = gtk_label_new ("Hello, world!");
+      gtk_container_add (GTK_CONTAINER (vbox), label);
+      GtkWidget *button = gtk_button_new_with_label ("Quit");
+      g_signal_connect (button, "clicked", G_CALLBACK (gtk_main_quit), NULL);
+      gtk_container_add (GTK_CONTAINER (vbox), button);
+      gtk_widget_show (button);
+      gtk_widget_show (label);
+      gtk_widget_show (vbox);
+      gtk_widget_show (window);
+      gtk_main ();
+      return 0;
+    }
+  \end{lstlisting}
+
+  \vspace*{-6cm}\strut\hfill
+  \includegraphics[scale=0.85]{hello-gtk.png}\\[2cm]
+  \begin{flushright}
+    \normalsize\bf Praktikumsversuch:\\
+    Objektorientiertes Zeichenprogramm
+  \end{flushright}
+  
+\end{frame}
+
+\subsection{Ausblick: C++}
+
+\begin{frame}[fragile]
+  \showsubsection
+
+  \begin{center}
+    \begin{minipage}{5cm}
+      \begin{lstlisting}[gobble=8]
+        ¡typedef struct
+        {
+          void (* print) (union t_object *this);
+        } t_base;¿
+      \end{lstlisting}
+    \end{minipage}\\[0.5cm]
+    \begin{minipage}{5.5cm}
+      \begin{lstlisting}[gobble=8]
+        ¡typedef struct
+        {
+          void (* print) (...);
+          int content;
+        } t_integer;¿
+      \end{lstlisting}
+    \end{minipage}
+    \begin{minipage}{5cm}
+      \begin{lstlisting}[gobble=8]
+        ¡typedef struct
+        {
+          void (* print) (union t_object *this);
+          char *content;
+        } t_string;¿
+      \end{lstlisting}
+    \end{minipage}
+  \end{center}
+  
+\end{frame}
+
+\begin{frame}[fragile]
+  \showsubsection
+
+  \begin{center}
+    \begin{minipage}{5cm}
+      \begin{lstlisting}[gobble=8]
+        ¡struct TBase
+        {
+          virtual void print (void);
+        };¿
+      \end{lstlisting}
+    \end{minipage}\\[0.5cm]
+    \begin{minipage}{5.5cm}
+      \begin{lstlisting}[gobble=8]
+        ¡struct TInteger: public TBase
+        {
+          virtual void print (void);
+          int content;
+        };¿
+      \end{lstlisting}
+    \end{minipage}
+    \begin{minipage}{5cm}
+      \begin{lstlisting}[gobble=8]
+        ¡struct TString: public TBase
+        {
+          virtual void print (void);
+          char *content;
+        };¿
+      \end{lstlisting}
+    \end{minipage}
+  \end{center}
+  
+\end{frame}
+
+\fi
+
+\end{document}
diff --git a/20200109/landau-symbols-2.pdf b/20200109/landau-symbols-2.pdf
new file mode 120000
index 0000000000000000000000000000000000000000..6b458b6efd8e274824a6dfcaabc4b9c27d196dc4
--- /dev/null
+++ b/20200109/landau-symbols-2.pdf
@@ -0,0 +1 @@
+../common/landau-symbols-2.pdf
\ No newline at end of file
diff --git a/20200109/landau-symbols-3.pdf b/20200109/landau-symbols-3.pdf
new file mode 120000
index 0000000000000000000000000000000000000000..46efa409b35ff5df763c744a423599cba515d886
--- /dev/null
+++ b/20200109/landau-symbols-3.pdf
@@ -0,0 +1 @@
+../common/landau-symbols-3.pdf
\ No newline at end of file
diff --git a/20200109/landau-symbols.pdf b/20200109/landau-symbols.pdf
new file mode 120000
index 0000000000000000000000000000000000000000..ca145425bf07439c680632aa0663f84be601a565
--- /dev/null
+++ b/20200109/landau-symbols.pdf
@@ -0,0 +1 @@
+../common/landau-symbols.pdf
\ No newline at end of file
diff --git a/20200109/names.h b/20200109/names.h
new file mode 100644
index 0000000000000000000000000000000000000000..a265ff4141a2cc578d3f6f402822a2dbbd5cea90
--- /dev/null
+++ b/20200109/names.h
@@ -0,0 +1,50 @@
+"Michael",    "Laura",
+"Elias",      "Julia",
+"Luca",       "Anna",
+"Liam",       "Emma",
+"Alexander",  "Lena",
+"Noah",       "Vanessa",
+"Jonas",      "Lea",
+"Marcel",     "Mila",
+"Daniel",     "Lisa",
+"David",      "Lina",
+"Milan",      "Sarah",
+"Julian",     "Alina",
+"Linus",      "Emilia",
+"Thomas",     "Nina",
+"Samuel",     "Elena",
+"Levin",      "Lara",
+"Levi",       "Melanie",
+"Jan",        "Hannah",
+"Lukas",      "Sandra",
+"Tim",        "Leonie",
+"Patrick",    "Sophie",
+"Marvin",     "Mia",
+"Andreas",    "Amelie",
+"Leon",       "Selina",
+"Tobias",     "Luisa",
+"Simon",      "Maria",
+"Valentin",   "Jana",
+"Robin",      "Johanna",
+"Paul",       "Marie",
+"Markus",     "Milena",
+"Benjamin",   "Melina",
+"Stefan",     "Michelle",
+"Felix",      "Emily",
+"Florian",    "Renesmee",
+"Fabian",     "Aylin",
+"Emil",       "Jessica",
+"Aaron",      "Franziska",
+"Manuel",     "Jasmin",
+"Christian",  "Fiona",
+"Dominik",    "Sina",
+"Joshua",     "Jennifer",
+"Moritz",     "Claudia",
+"Sebastian",  "Nicole",
+"Peter",      "Annika",
+"Philipp",    "Sophia",
+"Max",        "Katharina",
+"Johannes",   "Isabella",
+"Finn",       "Nele",
+"Adrian",     "Elisabeth",
+"Martin",     "Pia",
diff --git a/20200109/objects-1.c b/20200109/objects-1.c
new file mode 100644
index 0000000000000000000000000000000000000000..1a628668fd7b8fb3a0d9886ac14e8e909bc23793
--- /dev/null
+++ b/20200109/objects-1.c
@@ -0,0 +1,28 @@
+#include <stdio.h>
+
+typedef struct
+{
+  int type;
+} t_base;
+
+typedef struct
+{
+  int type;
+  int content;
+} t_integer;
+
+typedef struct
+{
+  int type;
+  char *content;
+} t_string;
+
+int main (void)
+{
+  t_integer i = { 1, 42 };
+  t_string s = { 2, "Hello, world!" };
+
+  t_base *object[] = { &i, &s };
+
+  return 0;
+}
diff --git a/20200109/objects-2.c b/20200109/objects-2.c
new file mode 100644
index 0000000000000000000000000000000000000000..a47cfb4276085399afb86795d04b1f6ae20c95bf
--- /dev/null
+++ b/20200109/objects-2.c
@@ -0,0 +1,28 @@
+#include <stdio.h>
+
+typedef struct
+{
+  int type;
+} t_base;
+
+typedef struct
+{
+  int type;
+  int content;
+} t_integer;
+
+typedef struct
+{
+  int type;
+  char *content;
+} t_string;
+
+int main (void)
+{
+  t_integer i = { 1, 42 };
+  t_string s = { 2, "Hello, world!" };
+
+  t_base *object[] = { (t_base *) &i, (t_base *) &s };
+
+  return 0;
+}
diff --git a/20200109/objects-3.c b/20200109/objects-3.c
new file mode 100644
index 0000000000000000000000000000000000000000..ff9224c0767ccad39f5b1396720ee73b6a0455fb
--- /dev/null
+++ b/20200109/objects-3.c
@@ -0,0 +1,34 @@
+#include <stdio.h>
+
+typedef struct
+{
+  int type;
+} t_base;
+
+typedef struct
+{
+  int type;
+  int content;
+} t_integer;
+
+typedef struct
+{
+  int type;
+  char *content;
+} t_string;
+
+int main (void)
+{
+  t_integer i = { 1, 42 };
+  t_string s = { 2, "Hello, world!" };
+
+  t_base *object[] = { (t_base *) &i, (t_base *) &s };
+
+  for (int i = 0; i < 2; i++)
+    if (object[i]->type == 1)
+      printf ("Integer: %d\n", object[i]->content);
+    else if (object[i]->type == 2)
+      printf ("String: \"%s\"\n", object[i]->content);
+
+  return 0;
+}
diff --git a/20200109/objects-4.c b/20200109/objects-4.c
new file mode 100644
index 0000000000000000000000000000000000000000..ef7bffe80471d4b014258824421dce0557fc41dd
--- /dev/null
+++ b/20200109/objects-4.c
@@ -0,0 +1,34 @@
+#include <stdio.h>
+
+typedef struct
+{
+  int type;
+} t_base;
+
+typedef struct
+{
+  int type;
+  int content;
+} t_integer;
+
+typedef struct
+{
+  int type;
+  char *content;
+} t_string;
+
+int main (void)
+{
+  t_integer i = { 1, 42 };
+  t_string s = { 2, "Hello, world!" };
+
+  t_base *object[] = { (t_base *) &i, (t_base *) &s };
+
+  for (int i = 0; i < 2; i++)
+    if (object[i]->type == 1)
+      printf ("Integer: %d\n", (t_integer *) object[i]->content);
+    else if (object[i]->type == 2)
+      printf ("String: \"%s\"\n", (t_string *) object[i]->content);
+
+  return 0;
+}
diff --git a/20200109/objects-5.c b/20200109/objects-5.c
new file mode 100644
index 0000000000000000000000000000000000000000..820181d87e2a04b81cd2e03aa7980d970cd6c1a6
--- /dev/null
+++ b/20200109/objects-5.c
@@ -0,0 +1,34 @@
+#include <stdio.h>
+
+typedef struct
+{
+  int type;
+} t_base;
+
+typedef struct
+{
+  int type;
+  int content;
+} t_integer;
+
+typedef struct
+{
+  int type;
+  char *content;
+} t_string;
+
+int main (void)
+{
+  t_integer i = { 1, 42 };
+  t_string s = { 2, "Hello, world!" };
+
+  t_base *object[] = { (t_base *) &i, (t_base *) &s };
+
+  for (int i = 0; i < 2; i++)
+    if (object[i]->type == 1)
+      printf ("Integer: %d\n", ((t_integer *) object[i])->content);
+    else if (object[i]->type == 2)
+      printf ("String: \"%s\"\n", ((t_string *) object[i])->content);
+
+  return 0;
+}
diff --git a/20200109/pgslides.sty b/20200109/pgslides.sty
new file mode 120000
index 0000000000000000000000000000000000000000..da062f7454c898ca1bc89bc29f268d9f00b21e5b
--- /dev/null
+++ b/20200109/pgslides.sty
@@ -0,0 +1 @@
+../20200102/pgslides.sty
\ No newline at end of file
diff --git a/20200109/qsort-1.c b/20200109/qsort-1.c
new file mode 100644
index 0000000000000000000000000000000000000000..c5431b853862e62812016f4fd3a031eeb0b5c9df
--- /dev/null
+++ b/20200109/qsort-1.c
@@ -0,0 +1,70 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, char *pivot, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (name[i] == pivot)
+        printf (" <==");
+      else if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, char *pivot, int left, int right)
+{
+  int result = strcmp (name[left], pivot);
+  comparisons++;
+  display (name, pivot, left, right);
+  usleep (200000);
+  return result;
+}
+
+void quicksort (char **name, int left, int right)
+{
+  int p = (left + right) / 2;
+  char *pivot = name[p];
+  int l = left;
+  int r = right;
+  while (l < r)
+    {
+      while (l < r && compare (name, pivot, l, r - 1) < 0)
+        l++;
+      while (l < r && compare (name, pivot, r - 1, l) > 0)
+        r--;
+      if (l < r)
+        {
+          char *temp = name[r - 1];
+          name[r - 1] = name[l];
+          name[l] = temp;
+          l++;
+          r--;
+        }
+    }
+}
+
+void sort (char **name)
+{
+  int r = 0;
+  while (name[r])
+    r++;
+  quicksort (name, 0, r);
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  sort (name);
+  display (name, NULL, -1, -1);
+  return 0;
+}
diff --git a/20200109/qsort-2.c b/20200109/qsort-2.c
new file mode 100644
index 0000000000000000000000000000000000000000..cfdc2ec11a92a4292c9443e01453cce818e9e73a
--- /dev/null
+++ b/20200109/qsort-2.c
@@ -0,0 +1,72 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, char *pivot, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (name[i] == pivot)
+        printf (" <==");
+      else if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, char *pivot, int left, int right)
+{
+  int result = strcmp (name[left], pivot);
+  comparisons++;
+  display (name, pivot, left, right);
+  usleep (200000);
+  return result;
+}
+
+void quicksort (char **name, int left, int right)
+{
+  int p = (left + right) / 2;
+  char *pivot = name[p];
+  int l = left;
+  int r = right;
+  while (l < r)
+    {
+      while (l < r && compare (name, pivot, l, r - 1) < 0)
+        l++;
+      while (l < r && compare (name, pivot, r - 1, l) > 0)
+        r--;
+      if (l < r)
+        {
+          char *temp = name[r - 1];
+          name[r - 1] = name[l];
+          name[l] = temp;
+          l++;
+          r--;
+        }
+    }
+  if (l < right)
+    quicksort (name, l, right);
+}
+
+void sort (char **name)
+{
+  int r = 0;
+  while (name[r])
+    r++;
+  quicksort (name, 0, r);
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  sort (name);
+  display (name, NULL, -1, -1);
+  return 0;
+}
diff --git a/20200109/qsort-3.c b/20200109/qsort-3.c
new file mode 100644
index 0000000000000000000000000000000000000000..e6b7d9909473af6d8c13d3745dc6b07e8ea75699
--- /dev/null
+++ b/20200109/qsort-3.c
@@ -0,0 +1,74 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, char *pivot, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (name[i] == pivot)
+        printf (" <==");
+      else if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, char *pivot, int left, int right)
+{
+  int result = strcmp (name[left], pivot);
+  comparisons++;
+  display (name, pivot, left, right);
+  usleep (200000);
+  return result;
+}
+
+void quicksort (char **name, int left, int right)
+{
+  int p = (left + right) / 2;
+  char *pivot = name[p];
+  int l = left;
+  int r = right;
+  while (l < r)
+    {
+      while (l < r && compare (name, pivot, l, r - 1) < 0)
+        l++;
+      while (l < r && compare (name, pivot, r - 1, l) > 0)
+        r--;
+      if (l < r)
+        {
+          char *temp = name[r - 1];
+          name[r - 1] = name[l];
+          name[l] = temp;
+          l++;
+          r--;
+        }
+    }
+  if (r > left)
+    quicksort (name, left, r);
+  if (l < right)
+    quicksort (name, l, right);
+}
+
+void sort (char **name)
+{
+  int r = 0;
+  while (name[r])
+    r++;
+  quicksort (name, 0, r);
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  sort (name);
+  display (name, NULL, -1, -1);
+  return 0;
+}
diff --git a/20200109/sort-0.c b/20200109/sort-0.c
new file mode 100644
index 0000000000000000000000000000000000000000..70e0e717cbfd42a27bf90f419c216fa18b0783c7
--- /dev/null
+++ b/20200109/sort-0.c
@@ -0,0 +1,16 @@
+#include <stdio.h>
+
+int find_first (char **name)
+{
+  return 2;
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  int first = find_first (name);
+  printf ("%s\n", name[first]);
+  return 0;
+}
diff --git a/20200109/sort-1.c b/20200109/sort-1.c
new file mode 100644
index 0000000000000000000000000000000000000000..3f009d45657f84e462db48a67fa22821819216ad
--- /dev/null
+++ b/20200109/sort-1.c
@@ -0,0 +1,21 @@
+#include <stdio.h>
+#include <string.h>
+
+int find_first (char **name)
+{
+  int first = 0;
+  for (int i = 1; name[i]; i++)
+    if (strcmp (name[i], name[first]) < 0)
+      first = i;
+  return first;
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  int first = find_first (name);
+  printf ("%s\n", name[first]);
+  return 0;
+}
diff --git a/20200109/sort-2.c b/20200109/sort-2.c
new file mode 100644
index 0000000000000000000000000000000000000000..638e6e2caa670ceace0a854d0827292dfcb59ca5
--- /dev/null
+++ b/20200109/sort-2.c
@@ -0,0 +1,46 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200000);
+  return result;
+}
+
+int find_first (char **name)
+{
+  int first = 0;
+  for (int i = 1; name[i]; i++)
+    if (compare (name, i, first) < 0)
+      first = i;
+  return first;
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  int first = find_first (name);
+  display (name, first, -1);
+  return 0;
+}
diff --git a/20200109/sort-3.c b/20200109/sort-3.c
new file mode 100644
index 0000000000000000000000000000000000000000..430a6fc0e95fcb9bc225e3572566c8d187016130
--- /dev/null
+++ b/20200109/sort-3.c
@@ -0,0 +1,46 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200000);
+  return result;
+}
+
+int find_first (char **name, int i0)
+{
+  int first = i0;
+  for (int i = i0 + 1; name[i]; i++)
+    if (compare (name, i, first) < 0)
+      first = i;
+  return first;
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  int first = find_first (name, 0);
+  display (name, first, -1);
+  return 0;
+}
diff --git a/20200109/sort-4.c b/20200109/sort-4.c
new file mode 100644
index 0000000000000000000000000000000000000000..19d4f416a2d30c5181ad289fe1d0dcba91ee81cf
--- /dev/null
+++ b/20200109/sort-4.c
@@ -0,0 +1,59 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200000);
+  return result;
+}
+
+int find_first (char **name, int i0)
+{
+  int first = i0;
+  for (int i = i0 + 1; name[i]; i++)
+    if (compare (name, i, first) < 0)
+      first = i;
+  return first;
+}
+
+void sort (char **name)
+{
+  int sorted = 0;
+  while (name[sorted])
+    {
+      int first = find_first (name, sorted);
+      char *temp = name[sorted];
+      name[sorted] = name[first];
+      name[first] = temp;
+      sorted++;
+    }
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  sort (name);
+  display (name, -1, -1);
+  return 0;
+}
diff --git a/20200109/sort-5.c b/20200109/sort-5.c
new file mode 100644
index 0000000000000000000000000000000000000000..f0742bc8665d0b13edf4ad4ad3fe4790c1e6b929
--- /dev/null
+++ b/20200109/sort-5.c
@@ -0,0 +1,60 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200);
+  return result;
+}
+
+int find_first (char **name, int i0)
+{
+  int first = i0;
+  for (int i = i0 + 1; name[i]; i++)
+    if (compare (name, i, first) < 0)
+      first = i;
+  return first;
+}
+
+void sort (char **name)
+{
+  int sorted = 0;
+  while (name[sorted])
+    {
+      int first = find_first (name, sorted);
+      char *temp = name[sorted];
+      name[sorted] = name[first];
+      name[first] = temp;
+      sorted++;
+    }
+}
+
+int main (void)
+{
+  char *name[] = {
+                   #include "names.h"
+                   NULL
+                 };
+  sort (name);
+  display (name, -1, -1);
+  return 0;
+}
diff --git a/20200109/sort-6.c b/20200109/sort-6.c
new file mode 100644
index 0000000000000000000000000000000000000000..94a1a16abfacda7bb728f8d3317cd00b4cf8ccde
--- /dev/null
+++ b/20200109/sort-6.c
@@ -0,0 +1,60 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+//  display (name, left, right);
+//  usleep (200);
+  return result;
+}
+
+int find_first (char **name, int i0)
+{
+  int first = i0;
+  for (int i = i0 + 1; name[i]; i++)
+    if (compare (name, i, first) < 0)
+      first = i;
+  return first;
+}
+
+void sort (char **name)
+{
+  int sorted = 0;
+  while (name[sorted])
+    {
+      int first = find_first (name, sorted);
+      char *temp = name[sorted];
+      name[sorted] = name[first];
+      name[first] = temp;
+      sorted++;
+    }
+}
+
+int main (void)
+{
+  char *name[] = {
+                   #include "names.h"
+                   NULL
+                 };
+  sort (name);
+  display (name, -1, -1);
+  return 0;
+}
diff --git a/20200109/sort-7.c b/20200109/sort-7.c
new file mode 100644
index 0000000000000000000000000000000000000000..46132dd247a061dda0e5ebade9c5b818a1a74fcb
--- /dev/null
+++ b/20200109/sort-7.c
@@ -0,0 +1,53 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200000);
+  return result;
+}
+
+void sort (char **name)
+{
+  int sorted = 0;
+  while (name[sorted])
+    {
+      int first = sorted;
+      for (int i = sorted + 1; name[i]; i++)
+        if (compare (name, i, first) < 0)
+          first = i;
+      char *temp = name[sorted];
+      name[sorted] = name[first];
+      name[first] = temp;
+      sorted++;
+    }
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  sort (name);
+  display (name, -1, -1);
+  return 0;
+}