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Thread: rounding numbers...

  1. #1
    Senior Member
    Join Date
    Aug 2004
    NC, USA

    rounding numbers...

    Alright I know how to round a number, but ... I don't know what else to call this.

    I get a number simular to 308,916.82 ... I don't have a problen doing th math to round that up ... Math.ceil ... my problem is making that number flat to the next position down like: 310,000. So if I had 1152 i'd want it to be 1200. If I had 4,500,345 I'd want 4,600,000. Make sense?

    I hope so ... can anyone help me with this?

  2. #2
    Senior Member jbum's Avatar
    Join Date
    Feb 2004
    Los Angeles
    First off, to round a number up to the next 100, you would do this:

    n = Math.ceil(n/100)*100;

    In your case, however, you don't want to round to 100. In the case of 1152, you want to round to the next 100. But in the case of 4,500,345, you want to round to the next 100,000.

    You can use the Math.log() function to find the appropriate power of 10 for the number you are rounding.

    To find the logarithm, base 10 of a number N, you use:

    power10 = Math.log(n)/Math.log(10);

    In your case, you appear to be using this:

    power10 = Math.floor(Math.log(n)/Math.log(10))-1;

    If you then raise 10 to that power, you'll get the rounding number you desire.

    roundScale = Math.pow(10, power10);

    Here's the code:


    function myRoundUp(n)
    // next highest power of 10 for this number
    power10 = Math.floor(Math.log(n)/Math.log(10))-1;
    // 10 ^ power10
    roundScale = Math.pow(10,power10);
    trace('roundScale = ' + roundScale);
    n = Math.ceil(n/roundScale) * roundScale;
    return n;

    trace( 1152 +": " + myRoundUp( 1152 ));
    trace( 4500345 +": " + myRoundUp( 4500345 ));

    This produces the desired result.
    Last edited by jbum; 02-22-2005 at 03:18 PM.

  3. #3
    Senior Member
    Join Date
    Aug 2004
    NC, USA
    thanks a ton ... ... all that will help me a ton in the future!

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