Programmer's Notes » programming technique http://programmersnotes.info Notes on the web-development and artificial intelligence. Mon, 18 Jul 2011 13:20:46 +0000 en hourly 1 http://wordpress.org/?v=3.1 Nice trick with FOR loop http://programmersnotes.info/2009/02/20/nice-trick-with-for-loop/ http://programmersnotes.info/2009/02/20/nice-trick-with-for-loop/#comments Fri, 20 Feb 2009 07:28:57 +0000 Konstantin Mirin http://konstantin.takeforce.net/?p=8 Yet Another Related Posts Plugin.]]> Recently I’ve learned one nice trick with for loop. When you use it, you should know he number of itereations. Most people do it like this:

  1.  
  2. $a = array(1,2,3,4,5);
  3. $s = sizeof($a);//you may use count(), but sizeof if 5% faster :)
  4. for ($i = 0; $i < $s; $i++)
  5. {
  6. //do something clever here
  7. echo $a[$i].‘
  8. ‘;
  9. }
  10.  

But this requires counting number of elements before using a loop. However, writing like this:

  1.  
  2. $a = array(1,2,3,4,5);
  3. for ($i = 0; $i < sizeof($a); $i++)
  4. {
  5. //do something clever here
  6. echo $a[$i].‘
  7. ‘;
  8. }
  9.  

is really awful – you count number of elements on each iteration, never use this!
And nice trick I was talking about is using the “,” (comma) operator:

  1.  
  2. $a = array(1,2,3,4,5);
  3. for ($i = 0, $s = sizeof($a); $i < $s; $i++)
  4. {
  5. //do something clever here
  6. echo $a[$i].‘
  7. ‘;
  8. }
  9.  

See the initial condition: $i = 0, $s = sizeof($a) – we set $i to 0, as usual, and then – $s – to number of elements in array. Just several commands in one line.
Another usage of comma operator is:

  1.  
  2. for ($i = 0, $j = 0; $i < 10; $i++, $j+=5)
  3. {
  4. //each iteration we increment $i by 1 and $j by 5. Maybe you find some useful example of this :)
  5. }
  6.  

The above tricks apply to almost any language, that has similar for() syntax – C, C++, PHP, JS (not sure about Java, but it should be there also)

No related posts.

Related posts brought to you by Yet Another Related Posts Plugin.

]]> http://programmersnotes.info/2009/02/20/nice-trick-with-for-loop/feed/ 7