*******************************************************
 Statement - Display Day of the month.
 Programmer - Nirbhay Singh
 Written For - https://technosoft portal.wixite.com/welcome
 *******************************************************/

#include<stdio.h>
#include<conio.h>
#include<math.h>

int fm(int date, int month, int year) {
 int fmonth, leap;
 
 //leap function 1 for leap & 0 for non-leap
 if ((year % 100 == 0) && (year % 400 != 0))
 leap = 0;
 else if (year % 4 == 0)
 leap = 1;
 else
 leap = 0;
 
 fmonth = 3 + (2 - leap) * ((month + 2) / (2 * month))
 + (5 * month + month / 9) / 2;
 
 //bring it in range of 0 to 6
 fmonth = fmonth % 7;
 
 return fmonth;
}

//----------------------------------------------
int day_of_week(int date, int month, int year) {
 
 int dayOfWeek;
 int YY = year % 100;
 int century = year / 100;
 
 printf("\nDate: %d/%d/%d \n", date, month, year);
 
 dayOfWeek = 1.25 * YY + fm(date, month, year) + date - 2 * (century % 4);
 
 //remainder on division by 7
 dayOfWeek = dayOfWeek % 7;
 
 switch (dayOfWeek) {
 case 0:
 printf("weekday = Saturday");
 break;
 case 1:
 printf("weekday = Sunday");
 break;
 case 2:
 printf("weekday = Monday");
 break;
 case 3:
 printf("weekday = Tuesday");
 break;
 case 4:
 printf("weekday = Wednesday");
 break;
 case 5:
 printf("weekday = Thursday");
 break;
 case 6:
 printf("weekday = Friday");
 break;
 default:
 printf("Incorrect data");
 }
 return 0;
}
//------------------------------------------
void main() {
 int date, month, year;
 clrscr();
 
 printf("\nEnter the year ");
 scanf("%d", &year);
 
 printf("\nEnter the month ");
 scanf("%d", &month);
 
 printf("\nEnter the date ");
 scanf("%d", &date);
 
 day_of_week(date, month, year);
 
 getch();
}

/**********
Output :

Enter the year 2015
Enter the month 12
Enter the date 16
Date: 16/12/2015
weekday = Wednesday

************/