C Program to check if a date is valid or not

In C programming, validating a date requires checking multiple constraints including day, month, year ranges, leap years, and month-specific day limits. A valid date should range from 1/1/1800 to 31/12/9999.

Syntax

int datevalid(int day, int month, int year);
int isleap(int year);

Date Validation Constraints

• Date must be between 1 and 31
• Month must be between 1 and 12
• Year must be between 1800 and 9999
• April, June, September, November have maximum 30 days
• February has 29 days in leap years, 28 days otherwise

Example: Complete Date Validation

This program implements comprehensive date validation with leap year checking −

#include <stdio.h>
#define MAX_YEAR 9999
#define MIN_YEAR 1800

// Function to check if year is leap year
int isLeapYear(int year) {
    if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0))
        return 1;
    else
        return 0;
}

// Function to validate date
int isValidDate(int day, int month, int year) {
    // Check year range
    if (year < MIN_YEAR || year > MAX_YEAR)
        return 0;
    
    // Check month range
    if (month < 1 || month > 12)
        return 0;
    
    // Check day range
    if (day < 1 || day > 31)
        return 0;
    
    // Check February
    if (month == 2) {
        if (isLeapYear(year)) {
            return (day <= 29);
        } else {
            return (day <= 28);
        }
    }
    
    // Check months with 30 days
    if (month == 4 || month == 6 || month == 9 || month == 11) {
        return (day <= 30);
    }
    
    // All other months have 31 days
    return 1;
}

int main() {
    int day1 = 29, month1 = 11, year1 = 2002;
    int day2 = 29, month2 = 2, year2 = 2001;
    int day3 = 29, month3 = 2, year3 = 2004;
    
    printf("Date %d/%d/%d: ", day1, month1, year1);
    if (isValidDate(day1, month1, year1))
        printf("Valid<br>");
    else
        printf("Invalid<br>");
    
    printf("Date %d/%d/%d: ", day2, month2, year2);
    if (isValidDate(day2, month2, year2))
        printf("Valid<br>");
    else
        printf("Invalid<br>");
    
    printf("Date %d/%d/%d: ", day3, month3, year3);
    if (isValidDate(day3, month3, year3))
        printf("Valid<br>");
    else
        printf("Invalid<br>");
    
    return 0;
}

Date 29/11/2002: Valid
Date 29/2/2001: Invalid
Date 29/2/2004: Valid

How It Works

• Leap Year Logic: A year is leap if divisible by 4 but not by 100, or divisible by 400
• Month Validation: Checks 30-day months (April, June, September, November) separately
• February Validation: Uses leap year check to determine maximum days (28 or 29)
• Range Validation: Ensures year is between 1800-9999

Conclusion

Date validation in C requires systematic checking of year range, month limits, and day constraints based on calendar rules. The leap year calculation is crucial for February validation.