when does a leap year start code example

Example: Check Leap Year

#include <iostream>
using namespace std;

int main() {
    int year;
    cout << "Enter a year: ";
    cin >> year;
    if (year % 4 == 0) {
        if (year % 100 == 0) {
            (year % 400 == 0) ?
            cout << year << " is a leap year." :
            cout << year << " is not a leap year.";
        }
        else
            cout << year << " is a leap year.";
    }
    else
        cout << year << " is not a leap year.";
    return 0;
}