note 114318 added to control-structures.for

Remember that for-loops don't always need to go 'forwards'. For example, let's say I have the following code: <?php for ($i = 0; $i < calculateLoopLength(); $i++) { doSomethingWith($i); } >? As other comments have pointed out, if "calculateLoopLength" will keep giving back the same value, it can be moved outside the loop: <?php $loopLength = calculateLoopLength(); for ($i=0; $i < $loopLength; $i++) { doSomethingWith($i); } ?> However, if the order the looping doesn't matter (ie. each iteration is independent) then we don't need to use an extra variable either, we can just count down (ie. loop 'backwards') instead: <?php for ($i=calculateLoopLength(); $i > 0; $i--) { doSomething($i); } ?> In fact, we can simplify this even more, since "$i > 0" is equivalent to "$i" (due to type casting): <?php for ($i=calculateLoopLength(); $i; $i--) { doSomething($i); } ?> Finally, we can switch to a 'pre-decrement' instead of a 'post-decrement' to be slightly more efficient (see, for example, http://dfox.me/2011/04/php-most-common-mistakes-part-2-using-post-increment-instead-of-pre-increment/ ): <?php for ($i = calculateLoopLength(); $i; --$i) { doSomething($i); } ?> In this case we could also replace the entire loop with a map, which might make your algorithm clearer (although this won't work if calculateLoopLength() == 0): <?php array_map('doSomething', range(0, calculateLoopLength() - 1)); ?> ---- Server IP: 72.52.91.14 Probable Submitter: 72.52.91.14 ---- Manual Page -- http://php.net/manual/en/control-structures.for.php Edit -- https://master.php.net/note/edit/114318 Del: integrated -- https://master.php.net/note/delete/114318/integrated Del: useless -- https://master.php.net/note/delete/114318/useless Del: bad code -- https://master.php.net/note/delete/114318/bad+code Del: spam -- https://master.php.net/note/delete/114318/spam Del: non-english -- https://master.php.net/note/delete/114318/non-english Del: in docs -- https://master.php.net/note/delete/114318/in+docs Del: other reasons-- https://master.php.net/note/delete/114318 Reject -- https://master.php.net/note/reject/114318 Search -- https://master.php.net/manage/user-notes.php