Day of the Week using Date

day.c

#include <stdio.h>

char* cal_day(int y, int m, int d)
{
    char* days[]={"Sunday","Monday","Tuesday","Wednesday","Thursday", "Friday","Saturday"};
    int a=(14-m)/12;
    y=y-a;
    m=m+12*a-2;
    return days[ (d + y + y/4 - y/100 + y/400 + (31*m)/12) % 7];
}