как сравнивать даты?

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>
#include <math.h>
 
int main(void){
    time_t tToday, tNeeded;
    struct tm stToday = { 0 }, stNeeded = { 0 };
    double dblDiff;
    int sign = 0;
 
    tToday = time(NULL);
    stToday = *(localtime(&tToday));
 
    printf("Enter date in format dd/mm/yyyy: ");
    if ( scanf("%d/%d/%d", &stNeeded.tm_mday, &stNeeded.tm_mon, &stNeeded.tm_year) != 3 ){
        printf("Wrong date format!\n");
        exit(1);
    }
    stNeeded.tm_mon -= 1;
    stNeeded.tm_year -= 1900;
    stNeeded.tm_min = 1;
    if ( ( tNeeded = mktime(&stNeeded) ) == -1 ){
        printf("Error while calculate time.\n");
        exit(1);
    }
 
    if ( ( dblDiff = difftime(tToday, tNeeded) ) < 0.0 ){
        sign = 1;
        dblDiff = fabs(dblDiff);
    }
    dblDiff /= 60.0 * 60.0 * 24.0;
 
    printf("Today is %02d/%02d/%4d\n", stToday.tm_mday, stToday.tm_mon + 1, stToday.tm_year + 1900);
    printf("Entered date is %.0f days %s\n", ( sign ) ? ceil(dblDiff) : floor(dblDiff), ( sign ) ? "after" : "before");
 
    exit(0);
}

typedef struct
{
   int d;
   int m;
   int y;
} Date;
 
int datecmp(Date *d1, Date *d2)
{
   /* здесь сравнить поля структур и вернуть некоторое значение */
}

#include <stdio.h>
 
typedef struct
{
   int d;
   int m;
   int y;
} Date;
 
int datecmp(Date *d1, Date *d2)
{
   /* здесь сравнить поля структур и вернуть некоторое значение */
    return ( d1->y != d2->y ) ? d1->y - d2->y : ( d1->m != d2->m ) ? d1->m - d2->m : d1->d - d2->d;
}
 
int main(void){
    Date a = { 26, 8, 2010 }, b = { 25, 8, 2010 }, c = { 27, 8, 2010 }, d = { 26, 8, 2010 };
    int cmp;
 
    printf("A = %02d/%02d/%4d\n", a.d, a.m, a.y);
    printf("B = %02d/%02d/%4d\n", b.d, b.m, b.y);
    printf("C = %02d/%02d/%4d\n", c.d, c.m, c.y);
    printf("D = %02d/%02d/%4d\n", d.d, d.m, d.y);
 
    cmp = datecmp(&a, &b);
    printf("A is %s B\n", ( ! cmp ) ? "same as" : ( cmp < 0 ) ? "before" : "after");
    cmp = datecmp(&a, &c);
    printf("A is %s C\n", ( ! cmp ) ? "same as" : ( cmp < 0 ) ? "before" : "after");
    cmp = datecmp(&a, &d);
    printf("A is %s D\n", ( ! cmp ) ? "same as" : ( cmp < 0 ) ? "before" : "after");
 
    return 0;
}

for(i=0;i<size;i++){
     p=strtok(dates[i],"/"); // в dates хранятся все даты в формате char
     date[i].day=atoi(p); //здесь видимо происходит ошибка..
     cont=0;
        while((p=strtok(NULL,"/"))!=NULL)
             if(cont<1){
             date[i].month=atoi(p); 
             cont++;
             }else
             date[i].year=atoi(p); 
     }

...
if ( sscanf(dates[i], "%d/%d/%d", &date[i].day, &date[i].month, &date[i].year) != 3 ){
  // неверный формат
}
...