subtraction in a php while loop

I'd like to think I'm 开发者_高级运维far from a PHP novice, but for some reason I cannot get the following to work. I'm trying to subtract a value from a number using a PHP while loop.

The code is below, but it only seems to be subtracting the first value.

I've obviously initiated a mysql query, and then have the following code:

 $scMins = 500;
 while($f=mysql_fetch_object($r)){

  $duration = $f->duration;

  $scRem = ($scMins - $duration);


 }


 return $scRem;

but its just notn working.

Any help would be MUCH appreciated.

Thanks, Nick

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You always subtract from the initial value scMins

$scRem = 500;
while($f=mysql_fetch_object($r)){
  $duration = $f->duration;
  $scRem = ($scRem - $duration);
}

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What is $r?

If it returns nothing, then it most likely means that your loop is wrong. I'd check if your query actually returns something (or if it errors), the problem most likely lies there.

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In your while-loop the variables $scRem gets overwritten at each iteration. Try

$scRem += ($scMins - $duration);

But honestly it's not very clear what you are trying to achive, so this may be the wrong answer ;-)