what day given date

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

void whichDay(int );
int ex_yToNum(int);
int ex_y2ToNum(int);
int curr_yToNum(int ,int,int);
int isleap(int);

int main()
{
    int date,month,year;
    //input
    printf("enter date: ");
    scanf("%d",&date);
    printf("enter month: ");
    scanf("%d",&month);
    printf("enter year: ");
    scanf("%d",&year);


   /* if((isdigit(date)||isdigit(month)||isdigit(year))) //check if non integer value is given as input
    {
        printf("please enter only integer values");
        exit(0);
    }*/

    int exyear,exyear2;
    exyear=year%400;
    exyear2=exyear%100;
    exyear=exyear-exyear2;
    exyear2=exyear2-1;

    int num1,num2,num3;
    num1= ex_yToNum(exyear);
    num2= ex_y2ToNum(exyear2);
    num3= curr_yToNum(date,month,year);
    int sum=0;
    sum=num1+num2+num3;
    if(sum>=7)
        sum=sum-7;
    whichDay(sum);


    return 0;
}

int ex_yToNum(int exy)
{

    if(exy==400)
        return 0;
    else if (exy==300)
        return 1;
    else if (exy==200)
        return 3;
    else
        return 5;
}

int ex_y2ToNum(int exy2)
{

    int leap,ord,temp;
    leap= exy2/4;
    ord= exy2-leap;
    temp=leap*2+ord;

    return (temp%7);

}

int isleap(int y)
{

    if(y%400==0)
        return 1;
    else if(y%100==0)
        return 0;
    else if(y%4==0)
        return 1;
    else
        return 0;
}

int curr_yToNum(date,month,year)
{

    const int monthdays[12]={31,28,31,30,31,30,31,31,30,31,30,31};
    int i,sumdays=0;
    for(i=0;i<month-1;i++)
        sumdays+=monthdays[i];
    sumdays+=date;
    sumdays+=isleap(year);
    return sumdays%7;

}
void whichDay(int d)
{

    switch(d)
    {

    case 0 :
        printf("sunday");
        break;
    case 1:
        printf("monday");
        break;
    case 2:
        printf("tuesday");
        break;
    case 3:
        printf("wednesday");
        break;
    case 4:
        printf("thursday");
        break;
    case 5:
        printf("friday");
        break;
    case 6:
        printf("saturday");
        break;
    default: printf("some error");
    }
}