/************************************************
 Program to check whether a date is valid or not 
 * 
 * Enter a date (MM/DD/YYYY) :05/30/2002
 * Date is valid.
 * 
 * Enter a date (MM/DD/YYYY) :02/29/2001
 * Date is invalid.
 *************************************************/

#include<stdio.h> // include stdio.h library

int main(void) 
{
    int day, mon, year, is_leap = 0, is_valid = 1;

    printf("Enter a date (MM/DD/YYYY) :\n");
    scanf("%d/%d/%d", &mon, &day, &year);

    if (year >= 1800 && year <= 9999) 
    {

        //  check whether year is a leap year
        if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) 
        {
            is_leap = 1;
        }

        // check whether mon is between 1 and 12
        if(mon >= 1 && mon <= 12)
        {
            // check for days in feb
            if (mon == 2)
            {
                if (is_leap && day == 29) 
                {
                    is_valid = 1;
                }
                else if (day > 28) 
                {
                    is_valid = 0;
                }
            }

            // check for days in April, June, September and November
            else if (mon == 4 || mon == 6 || mon == 9 || mon == 11) 
            {
                if (day > 30)
                {
                    is_valid = 0;
                }
            }

            // check for days in rest of the months 
            // i.e Jan, Mar, May, July, Aug, Oct, Dec
            else if(day > 31)
            {            
                is_valid = 0;
            }        
        }

        else
        {
            is_valid = 0;
        }

    }
    else
    {
        is_valid = 0;
    }

    if(is_valid)
    {
        printf("Date is valid.");
    }

    else
    {
        printf("Date is invalid.");
    }

    return 0; // return 0 to operating system
}