If you input the date, the code will tell what day it will be.

date.c

#include<conio.h>
#include<stdio.h>
void main()
{
    int k,m,d,c,f,day,day1,i;
    
    printf("day=\n");
    scanf("%d",&k);

    printf("Type the following codes for the required month\nMarch-1\t\tApril-2\t\tMay-3\t\tJune-4\n");
    printf("July-5\t\tAUgust-6\tSeptember-7\tOctober-8\n");
    printf("November-9\tDecember-10\tJanuary-11\tFebraury-12\n");
    scanf("%d",&m);

    printf("Last 2 digits of year=\n");
    scanf("%d",&d);

    printf("first 2 digits of year=\n");
    scanf("%d",&c);

    if(m==11 || m==12)
    d=d-1;

    
    f=k + ((13*m-1)/5) + d + (d/4) + (c/4) - (2*c);  /*Zellers Rule*/

    day=f%7;
    
    
    if(day<0)
    {
        for(i=0;i<7;i++)
        {
           day=day-i;
           if (day%7==0)
             { 
              day=day-day1;
             }
            i++;
        }
    }

    
     if(m==11 || m==12)
     {
         m=m-10;
         d=d+1;
     }
     else
     {
         m=m+2;
     }
     


    if (day==0)
    printf("\n%d/%d/%d%d is Sunday",k,m,c,d);
    else if (day==1)
    printf("\n%d/%d/%d%d is Monday",k,m,c,d);
    else if (day==2)
    printf("\n%d/%d/%d%d is Tuesday",k,m,c,d);
    else if (day==3)
    printf("\n%d/%d/%d%d is Wednesday",k,m,c,d);
    else if (day==4)
    printf("\n%d/%d/%d%d is Thursday",k,m,c,d);
    else if (day==5)
    printf("\n%d/%d/%d%d is Friday",k,m,c,d);
    else if (day==6)
    printf("\n%d/%d/%d%d is Saturday",k,m,c,d);
    
}

OUTPUT

day=
16
Type the following codes for the required month
March-1         April-2         May-3           June-4
July-5          AUgust-6        September-7     October-8
November-9      December-10     January-11      Febraury-12
6
Last 2 digits of year=
19
first 2 digits of year=
20

16/8/2019 is Friday