gistfile1.c

#include <stdio.h>
#include <ctype.h>

int is_leap_year(int year);
int day_of_year(int day, int month, int year);
int main() {
    int day = 0, month = 0, year = 0;

    printf("Podaj date (dd/mm/rrrr): ");

    scanf("%d/%d/%d",&day,&month,&year);

    printf("Dzień roku: %d",day_of_year(day,month,year));

    return 0;
}
int is_leap_year(int year){
    return (year % 4 ==0 && year %100 != 0) || year %400 ==0;
}
int get_month_days(int month,int year)
{
    if(month == 2)
            return 28+is_leap_year(year);
    unsigned int magic_number=0xAD5;
    magic_number = magic_number >> (month -1);
    if(magic_number & 1)
        return 31;
    else
        return 30;
}
int day_of_year(int day, int month, int year)
{
   int number_days=0,i;

   for (i=1;i<month;i++)
   {
      number_days+=get_month_days(i,year);
   }
   return number_days+day;
}