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Thread: Method to reverse String using While Loop

  1. #1
    Junior Member Montrell79's Avatar
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    Cool Method to reverse String using While Loop

    Hello, I am trying to create a program that will output the reverse of any string of integers. I got the program to work with some help from another forum, but I'm just not understanding why it works.
    Specifically, what purpose is the + 10 * result serving?
    I can tell that it is allowing result to store all the modulus results instead of just replacing them as the loops continues, but I want to understand why.
    I've tested the program without the +10*result, and it doesn't work because the return result will only store the last result. For example, if you enter 654, instead of getting 456, you would only get 4 since result keeps getting replaced by 6, 5 & 4.

    Here is the code: I appreciate any feedback or help!

    public static void main(String[] args) {
    String num1Str;
    int num1, num2;


    num1Str = JOptionPane.showInputDialog("Enter a positive integer");
    num1 = Integer.parseInt(num1Str);

    //call method
    num2 = reverse(num1);


    JOptionPane.showMessageDialog(null, "The reversed integer for " + num1 + " is " + num2);
    }


    public static int reverse(int myInput){

    int result = 0 ;
    while ( myInput > 0 )
    {
    result = myInput % 10 + 10 * result;
    myInput /= 10 ;
    }
    return result ;

    }


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Method to reverse String using While Loop

    what purpose is the 10 * result
    Look at the value of result and the value of result*10. The second one has all the digits shifted left 1 decimal digit and a 0 added on the right.

    Think about how you would build a number given a bunch of digits and a power of 10 for each.
    2*1000 + 3 * 100 + 4 * 10 + 5
    What if I give you the numbers one by one: 2 and then 3 and then 4 and then 5. what is the result
    Now what if there are only 2 numbers: 2 and 3 and I give them to you one at a time.
    Now suppose there are 8 numbers one at a time.
    etc
    Each new number is the old*10 plus the new number.
    Last edited by Norm; February 22nd, 2012 at 02:52 PM.

  3. The Following User Says Thank You to Norm For This Useful Post:

    Montrell79 (February 22nd, 2012)

  4. #3
    Junior Member Montrell79's Avatar
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    Default Re: Method to reverse String using While Loop

    Thanks Norm! Got it now

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