Actionscript Cookbook

5.3. Rounding Numbers

Problem

You want to round a number to the nearest integer, decimal place, or interval (such as to the nearest multiple of 5).

Solution

Use Math.round( ) to round a number to the nearest integer. Use Math.floor( ) and Math.ceil( ) to round a number down or up, respectively. Create a custom roundTo( ) method to round a number to a specified number of decimal places or to a specified multiple.

Discussion

There are numerous reasons to round numbers. For example, when displaying the results of a calculation, you might display only the intended precision. Because all arithmetic in ActionScript is performed with floating-point numbers, some calculations result in unexpected floating-point numbers that must be rounded. For example, the result of a calculation may be 3.9999999 in practice even though it should be 4.0 in theory.

The Math.round( ) method returns the nearest integer value of any parameter passed to it:

trace(Math.round(204.499));  // Displays: 204
trace(Math.round(401.5));    // Displays: 402

The Math.floor( ) method rounds down, and the Math.ceil( ) method rounds up:

trace(Math.floor(204.99));   // Displays: 204
trace(Math.ceil(401.01));    // Displays: 402

To round a number to the nearest decimal place:

1. Decide the number of decimal places to which you want to round. For example, if you want to round 90.337 to 90.34, then you will round to two decimal places, which means that you will round to the nearest .01.

2. Divide the input value by the number chosen in Step 1 (in ...