For Loop: Leap year

Question

I'm trying to write a program that displays ten leap years per line until the year 2100.

The code I have so far is this:

public class leapYear {
public static void main (String args[]){
    int leapYear = 2001; // initialize leapYear variable to 2001

    if (leapYear <= 2100){
        for (int x = 0; x <= 10; x++){ // print ten leap years per line
            System.out.print(leapYear + " ");
            leapYear = leapYear + 4;
        }// end of for loop
        System.out.println(" ");
        int x = 0;
    } // end of if statement

}// end of main method

}// end of class

The output I get from the code is:

2001 2005 2009 2013 2017 2021 2025 2029 2033 2037 2041  

I'm having trouble finding a condition that will allow me to print the next series of leapYears on the following lines. Any guidance would be appreciate.

Answer 1

Change the if(leapYear <= 2100) line to while(leapYear <= 2100) .

The if statement will only execute once, meaning you print out 10 dates. A while loop will execute as many times as it takes for leapYear to be greater than 2100.

Answer 2

You are currently using an if statement to check whether or not you want to print something ( if (leapYear <= 2100) ). However, after your for-loop you want to check again whether there are still more leap years to print before reaching the year 2100 . This can be accomplished by using a while loop instead, ie while(leapYear < 2100) . (As 2100 is not a leap year, see below)

Additionally, it should be noted that 2004 is a better starting place for leap-years and 2100 is not a leap year (wheareas 2000 was). See the wiki for more information.

Second note unrelated to your problem, you can also use System.out.println(); (so without an argument) to print the newline you are after.

Third and final, the line int x = 0; is not necessary as the counter x in your for loop no longer exists outside of that loop.

Answer 3

Your If statement is whats giving you the trouble, it only executes once. You need something like a while loop, or you could use a for loop like so,

                for (int leapYear = 2001; leapYear <= 2100; leapYear += 4) {
                    if((leapYear - 1) % 40 == 0) {
                        System.out.println(" ");
                    }
                    System.out.print(leapYear + " ");
                }

However I would like to point out that none of the years you print out are leap years. leap years are those divisible by 4 except when divisible by 100 except when also divisible by 400 (ie 2000 was a leap year 2004 was and 2100 won't be but 2400 will be) super confusing you may want to check this out on leap years.

Good luck!

Answer 4

You asked how to have 10 leap years print per line. To accomplish this, simply change:
if (leapYear <= 2100) {
To:
while (leapYear <= 2100) {

With the full working and tested example here:

public class LeapYear {
    public static void main(String[] args) {

        int leapYear = 2001; // initialize leapYear variable to 2001

        while (leapYear <= 2100) { // a simple change of "If" to "While" here
                                    // will do the trick
            for (int x = 0; x < 10; x++) {
                System.out.print(leapYear + " "); // print ten leap years per
                                                    // line
                leapYear = leapYear + 4;
            }
            System.out.println();
        } // end of while loop
    } // end of main method
}// end of class

That being said, I would recommend some of the things that have already been mentioned.

1 - There are some logic errors in your code that will incorrectly name some years leap years. See here for more information on Leap Years.

2 - If you try my example, you'll also notice that the leap years are shown past 2100. You'll need to figure out a way to correctly structure your code if you don't want the numbers to be displayed past 2100.

3 - I would strongly recommend you take a look at the GregorianCalendar class, as it will simplify your code to check for a leap year. However, if you are doing this to learn or for a school assignment, I would recommend looking at the link under number 1.

4 - More of an aside, but in your code you have:

leapYear = leapYear + 4

This can be simplified to:

leapYear += 4

Hopefully this helps clarify things for you.

Answer 5

Providing the correct implementation for leap year:

public void main(String[] args) {
    for(int year = 2001 ; year <= 2100 ; ++year) {
        if(isLeapYear(year)) {
            System.out.println(year);
        }
    }
}

public static boolean isLeapYear(int year) {
    if (year % 4 != 0) {
        return false;
    } else if (year % 400 == 0) {
        return true;
    } else if (year % 100 == 0) {
        return false;
    } else {
        return true;
    }
}

Answer 6

public static void main (String args[]){
    int leapYear = 2001; // initialize leapYear variable to 2001

    while (leapYear <= 2100){
        for (int x = 0; x < 10; x++){ // print ten leap years per line
            if (leapYear > 2100){ // if leapYear is over 2100, stop printing
                break;
            }
            System.out.print(leapYear + " ");
            leapYear = leapYear + 4;
        }// end of for loop
        System.out.println(" ");
        int x = 0;
    } // end of if statement

}// end of main method