WHILE vs. FOR loops

Joseph_Sliker

I don't have any formal training in programming but thanks to all the concrete help I have gotten here over the past several months, I've been able to do a lot of really neat, useful stuff at work with PHP & MySQL.

The more code I write, the more "abstract" questions are beginning to occur to me. Here's one that probably belongs in this section.

Sometimes I have been advised to write "while" loops, and at other times, "for" loops.

They seem very similar to me. What would be some fundamental reasons to use one over the other?

procoder

There are different occasiaons when the other one is better to use.

For example, for db querys i use while


while($row = $db->fetch_array)

this way, when $row = 0(no more rows), the while stops.

if i wanted to print 1-10 i would do

for($=0;$i<10;$i++) { echo $i; }

instead of

$i = 0
while($i<10) {
echo $i
$i++ }

while man: http://us4.php.net/while
for man: http://us4.php.net/manual/en/control-structures.for.php

laserlight

Simply put, for loops are usually used when there number of times to loop is known (perhaps not to you, but at least to the script).
While loops are usually used when that is not known.
Do while loops are usually used when you want the code within the loop to be executed at least once.

For infinite loops, one might use
for (;😉

There is also the foreach() construct, which can be used on arrays instead of the normal for or while loops.

drawmack

just think about it in english

If you want to loop for a specific amount of something (number of times being the most common) then use a for loop.

If you want to loop while something, or while not something, then use a while loop.

Do while should be use when you want something to execute at least once instead of a while loop.

foreach should be used when you for condition is the number of elements in an array.

Joseph_Sliker

That was a great set of replies! Thank you all very much. I'm reading my php & MySQL books in a kind of hit-or-miss fashion and have not come upon an organized presentation of this topic so far.

drawmack

try reading an intro to programming book this is a basic programming methodology that is not specific to php.

mystrymaster

any good recomendations on the intro to programming books?

I picked up php a couple months ago as well and would like to understand the intracacies and best practices as well

drawmack

contact your local college and ask them what books they use for: intro to programming & linear data structures classes.

mystrymaster

yeah duh - didn't even think of that