pvjc20/du3/program.c

#define __USE_XOPEN
#define _GNU_SOURCE

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

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) {
        puts("Neplatny datum");
        return 0;
    }

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

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