pvjc20/du3/program.c

#define __USE_XOPEN
#define _GNU_SOURCE

#include<stdio.h>
#include<time.h>
#include<stdlib.h>

#define max_yr 9999
#define min_yr 1900

int isleap(int y) {
   if (y % 4 != 0) {
      return 0;
   } else if (y % 100 != 0) {
      return 1;
   } else if (y % 400 != 0) {
      return 0;
   }

   return 1;
}

int datevalid(int d, int m, int y) {
   if(y < min_yr || y > max_yr) {
      return 0;
   }
   
   if(m < 1 || m > 12) {
      return 0;
   }
   
   if(d < 1 || d > 31) {
      return 0;
   }

   if (m == 2) {
      if (isleap(y)) {
         if (d > 29) {
            return 0;
         }
      } else {
         if (d > 28) {
            return 0;
         }
      }
   }

   if ( m == 4 || m == 6 || m == 9 || m == 11 ) {
      if(d <= 30) {
         return 1;
      } else {
         return 0;
      }
   }

   return 1;
}

int main() {
   char buffer[20];
   struct tm tm = {0};

   char *retval = fgets(buffer, sizeof(buffer), stdin);

   if (retval == 0) {
      puts("Neplatny datum");
      return 0;
   }

   retval = strptime(buffer, "%e.%m.%-Y", &tm);

   if (retval == 0 || datevalid(tm.tm_mday, tm.tm_mon + 1, tm.tm_year + 1900) == 0) {
      puts("Neplatny datum");
      return 0;
   }

   tm.tm_isdst = -1;
   tm.tm_mday += 7;

   if (mktime(&tm) == -1) {
      puts("Neplatny datum");
      return 0;
   }
   
   strftime(buffer, sizeof(buffer), "%e.%m.%-Y", &tm);
   puts(buffer);
   putc('\n', stdout);
   
   return 0;
}