C Program to Check Leap Year

In this article, you will learn and get code for checking whether any given year is a leap year or not. Before going to the program, here is the formula to check whether the given year is a leap year or not.

• year that is divisible by 4 but not by 100
• or a year that can be divided by 400.

To understand where this formula came from, refer to Leap Year Formula Explained. Now let's move on and implement it in a C program.

Leap Year Program in C

Now, I'm sure that you have a complete understanding of what the leap year is and how it gets calculated. So it's time to apply it to the program:

#include<stdio.h>
#include<conio.h>
int main()
{
    int year;
    printf("Enter Year: ");
    scanf("%d", &year);
    if((year%4==0) && (year%100!=0))
        printf("\nIt's a Leap Year");
    else if(year%400==0)
        printf("\nIt's a Leap Year");
    else
        printf("\nIt's not a Leap Year");
    getch();
    return 0;
}

This program was compiled and executed using the Code::Blocks IDE. Here is the first snapshot of the sample run:

Supply any year, say 2100, as input and press the ENTER key to see the output as shown in the snapshot given below:

It is a very simple program, and you can easily understand it as all the logic used behind leap year is described in the beginning of this article. So let's move on to another program using functions.

Using the C function, determine the leap year

This program will continue checking for leap years until the user wants to terminate it. Because we've added some extra code here, the user can now check the leap year any number of times at once. To check for leap years, this program uses a function. Let's have a look at it:

#include<stdio.h>
#include<conio.h>
int checkLeapFun(int);
int main()
{
    int year, lORn;
    char choice='y';
    while(choice=='y')
    {
        printf("Enter Year: ");
        scanf("%d", &year);
        lORn = checkLeapFun(year);
        if(lORn == 0)
            printf("It's a Leap Year");
        else
            printf("It's not a Leap Year");
        printf("\n\nWant to check more ? (y/n): ");
        scanf(" %c", &choice);
        printf("\n");
    }
    getch();
    return 0;
}
int checkLeapFun(int yr)
{
    if((yr%4==0) && (yr%100!=0))
        return 0;
    else if(yr%400==0)
        return 0;
    else
        return 1;
}

Here is a sample run of the above program:

In this way, you can continue checking until you want to terminate. To check for another year, simply press y (yes) and enter the year. And to terminate it, just enter n (for no) or any other character except y.

Program Explained

• Declare any two int (integer) variables, such as year and lORn (leap or not).
• Here year holds the year value entered by the user, and the lORn variable is used to get the return value of the function checkLeapFun().
• Declare another variable, say the choice of the char (character) type.
• Initialize it with y as its value.
• Here y is initialized as the initial value of choice, so to make the condition choice=='y' evaluates to be true (for the first time), enter into the while loop to process the code further.
• Inside the loop, scan the year value from the user, and pass it to the function checkLeapFun() with year as its parameter.
• Now inside the function, apply the condition of leap year and return its value accordingly.
• That is, if it is a leap year, then 0 gets returned, otherwise 1 gets returned and initialized to the lORn variable.
• After the return statement, program flow comes back inside the while loop of the main() function, and the return value gets initialized to lORn as told in the previous step.
• Use the if-else case to check and print the output according to the value of lORn.
• Now scan a user's character to see if he or she wants to check for another year or not.
• If you want to check for more, then press y; otherwise, press n.
• The input character gets initialized to the choice, and the program flow goes to the condition of the while loop.
• checks whether it is equal to y or not; if it is, the program flow goes inside the loop again; otherwise, the program flow terminates the loop and goes to the next statement written after the loop, which is gets();

Note: Use space before scanning the character as input because the %c conversion specifier won't automatically skip any leading whitespace. So, from the previous entry, if there is a stray newline in the input stream, the scanf() call will consume it immediately.

So here we have used:

scanf(" %c", &choice);

as a statement about scanning a character. Because the blank is in the format string, it tells scanf to skip any leading whitespace.

The same program in different languages

• C++ Check Leap Year
• Java Check Leap Year
• Python Check Leap Year

C Quiz