How do I add 0 to single digits in this java program?

Question

I am very new to Java. I have barely gotten through the basics (this is my first attempt at using a while loop) and now conveniently have a problem at work that can clearly be solved with programming. We need to add numbers to a print document in the format "xx-xx-xx" such that it will begin with 00-00-00 and end with 99-99-99. Specifically, I need to have leading zeros for the single digits.

I have managed to write a program that prints the numbers we need and I just found out I can output to a text file simply in command prompt (horrifically slow on this old computer using Windows XP and java 1.7), but I can't figure out how to add 0 in front of single digit numbers.

Here's what I have:

public class Numbers {
    public static void main(String[] args){
        int a = 0;
        int b = 0;
        int c = 0;
        while (a<100) {
            if(c<99){
                c = c+1;
                System.out.println(a + "-" + b + "-" + c);
            }
            else if(b<99) {
                c = 0;
                b = b+1;
                System.out.println(a + "-" + b + "-" + c);
            }
            else if(a<99) {
                c = 0;
                b = 0;
                a = a+1;
                System.out.println(a + "-" + b + "-" + c);
            }
        }
    }
}   

I have tried a couple of things, but I am most likely not implementing them correctly because, again, I have no idea what I'm doing. I understand that there is a way to format strings in general and there is a printf function and I know there is something you can do with %02d (I've seen String.format("%02d", myNumber) as an answer, but couldn't figure out exactly how to implement that in my code) and I read something about PrintStream and PrintWriter, etc, but I am not nearly experienced enough to know how to use all of that.

The real problem is that I don't exactly have a lot of time to work on this, unfortunately our clients all demand quick turnaround times (they were already asking for a sample yesterday afternoon, hours after we got the job). I'm sure I would eventually be able to figure it out and I will continue trying when I have time, but I also have other work to do and didn't have time last night.

I was thinking of rewriting the code to get rid of the dashes (thinking maybe the fact that there is a string already being printed prevents me from being able to format what I print) but I expect I will run into other problems there.

I would greatly appreciate any input and suggestions for further exploration of java and programming in general (I think I love learning more than just about anything else, I am constantly ravenous and can't be sated).

Answer 1

You can do,

System.out.printf("%02d-%02d-%02d\n", a, b, c);

instead of your println statements.

Answer 2

For a single integral type number a , use

System.out.printf("%02d-%02d-%02d\\n", a / 100 / 100 % 100, a / 100 % 100, a % 100);

would do it. The % 100 extracts the last two digits of the int s. The / is used to extract the bits of the number you need.

If you have three separate numbers a , b , and c , use

System.out.printf("%02d-%02d-%02d\\n", a % 100, b % 100, c % 100);

Answer 3

If you want custom outputs: use the command

System.out.printf();

in your case you need to use

System.out.printf("%02d-%02d-%02d",a,b,c);

instead of System.out.println(); statements