incdate-9.c

#include <stdio.h>

typedef struct
{
  char day, month;
  int year;
}
date;

void set_date (date *d)
{
  d->day = 28;
  d->month = 2;
  d->year = 2000;
}

void inc_date (date *d)
{
  d->day++;
  int days_in_month = 31;
  if (d->month == 2)
    {
      int is_leap_year = 0;
      if (d->year % 4 == 0)
        {
          is_leap_year = 1;
          if (d->year % 100 == 0)
            {
              is_leap_year = 0;
              if (d->year % 400 == 0)
                is_leap_year = 1;
            }
        }
      if (is_leap_year)
        days_in_month = 29;
      else
        days_in_month = 28;
    }
  else if (d->month == 4 || d->month == 6 || d->month == 9 || d->month == 11)
    days_in_month = 30;
  if (d->day > days_in_month)
    {
      d->month++;
      d->day = 1;
      if (d->month > 12)
        {
          d->year++;
          d->month = 1;
        }
    }
}

int main (void)
{
  date today;
  set_date (&today);
  inc_date (&today);
  printf ("%d.%d.%d\n", today.day, today.month, today.year);
  return 0;
}