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2.4. Rounding Floating-Point Numbers

2.4.3. Discussion

If a number falls exactly between two integers, its behavior is undefined:

$number = round(2.5);   // $number is 2 or 3!

Be careful! As we mention in Recipe 2.3, floating-point numbers don't always work out to exact values because of how they're stored internally by the computer. This can create situations in which the obvious answer isn't. A value you expect to have a decimal part of "0.5" might instead be ".499999...9" (with a whole bunch of 9s) or ".500000...1" (with many 0s and a trailing 1). If you want to ensure that a number is rounded up as you might expect, add a small delta value to it before rounding:

$delta = 0.0000001;
$number = round(2.5 + $delta);   // $number = 3

To keep a set number of digits after the decimal point, round( ) accepts an optional precision argument. For example, if you are calculating the total price for the items in a user's shopping cart:

$cart = 54.23;
$tax = $cart * .05;
$total = $cart + $tax;       // $total = 56.9415

$final = round($total, 2);   // $final = 56.94

2.4.4. See Also

Recipe 2.3 for information on comparing floating-point numbers; documentation on round( ) at http://www.php.net/round.

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