2.4. Operating on a Series of Integers
Problem
You want to apply a piece of code over a range of integers.
Solution
Use the range( )
function, which returns an array populated
with integers:
foreach(range($start,$end) as $i) { plot_point($i); }
Instead of using range( )
, it can be more
efficient to use a for
loop. Also, you can
increment using values other than 1. For example:
for ($i = $start; $i <= $end; $i += $increment) { plot_point($i); }
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 ...
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