Erweiterte Musterlösung zu Aufgabe 3b der Klausur vom 29.1.2016

exams/20160129/loesung-3b-extra.c

+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct
+{
+  char symbol;
+  int (*calculate) (int a, int b);
+}
+operation;
+
+operation *new_operation (void)
+{
+  operation *op = malloc (sizeof (operation));
+  op->symbol = '?';
+  op->calculate = NULL;
+  return op;
+}
+
+/* Virtuelle Methoden */
+
+int calculate_plus (int a, int b)
+{
+  return a + b;
+}
+
+int calculate_minus (int a, int b)
+{
+  return a - b;
+}
+
+int calculate_times (int a, int b)
+{
+  return a * b;
+}
+
+/* Konstruktoren */
+
+operation *new_plus ()
+{
+  operation *op = malloc (sizeof (operation));
+  op->symbol = '+';
+  op->calculate = calculate_plus;
+  return op;
+}
+
+operation *new_minus ()
+{
+  operation *op = malloc (sizeof (operation));
+  op->symbol = '-';
+  op->calculate = calculate_minus;
+  return op;
+}
+
+operation *new_times ()
+{
+  operation *op = malloc (sizeof (operation));
+  op->symbol = '*';
+  op->calculate = calculate_times;
+  return op;
+}
+
+/* Besonders ordentlich: Speicher wieder freigeben - Destruktor */
+
+void delete_operation (operation *op)
+{
+  if (op)
+    free (op);
+}
+
+int main (void)
+{
+  operation *op[4];
+  op[0] = new_plus ();
+  op[1] = new_minus ();
+  op[2] = new_times ();
+  op[3] = NULL;
+  for (int i = 0; op[i]; i++)
+    printf ("2 %c 3 = %d\n", op[i]->symbol, op[i]->calculate (2, 3));
+  for (int i = 0; op[i]; i++)
+    delete_operation (op[i]);
+  return 0;
+}