Operating on a Series of Integers (PHP Cookbook)

2.5.3. Discussion

Loops like this are common. For instance, you could be plotting a function and need to calculate the results for multiple points on the graph. Or, you could be NASA counting down until the launch of the Space Shuttle Columbia.

In the first example, range( ) returns an array with values from $start to $end. Then foreach pulls out each element and assigns it to $i inside of the loop. The advantage of using range( ) is its brevity, but this technique has a few disadvantages. For one, a large array can take up unnecessary memory. Also, you're forced to increment the series one number at a time, so you can't loop through a series of even integers, for example.

As of PHP 4.1, it is valid for $start to be larger than $end. In this case, the numbers returned by range( ) are in descending order. Also, you can use iterate over character sequences:

print_r(range('l', 'p'));
Array
(
    [0] => l
    [1] => m
    [2] => n
    [3] => o
    [4] => p
)

The for loop method just uses a single integer and avoids the array entirely. While it's longer, you have greater control over the loop, because you can increment and decrement $i more freely. Also, you can modify $i from inside the loop, something you can't do with range( ), because PHP reads in the entire array when it enters the loop, and changes to the array don't effect the sequence of elements.

2.5.4. See Also

Recipe 4.4 for details on initializing an array to a range of integers; documentation on range( ) at http://www.php.net/range.

2.5. Operating on a Series of Integers

2.5.1. Problem

2.5.2. Solution

2.5.3. Discussion

2.5.4. See Also