PHP while loop problems

Question

I am primarily a CSS and HTML guy but I have recently ventured into PHP.

I can't see why this script hangs:

$loop_Until = 10;

while($i < $loop_Until)
{
    // do some code here
    $loop_Until = $loop_Until + 1;
}

Can anyone please help?

Answer 1

This is causing an ifinate loop, youo will want to take a look at the php for loop. http://php.net/manual/en/control-structures.for.php

for($i= 1; $i< $loop_Until; ++$i) {
    // do some code here
}

You are increasing $loop_Until every time and never increaing $i therefore $i will always be less than $loop_Until

Answer 2

Fixed Code

$loop_Until = 10;
$i = 0;

    while($i < $loop_Until)
    {
        // do some code here
        $i = $i + 1;
    }

Explanation of your code:

// A variable called loop until is set to 10
$loop_Until = 10;  

// While the variable i is less than 10
// NOTE:  i is not set in code snippet, so we have no way of knowing what value it is, if it is greater than 10 it might be infinite
while($i < $loop_Until)
{
    // Increment the 10 value up 1 every time, i never changes!
    $loop_Until = $loop_Until + 1;
}

Answer 3

Simplest solution: Replace your "+" with a "-". This will cause the loop to end. Like this:

$loop_Until = 10;

while($i < $loop_Until)
{
    // do some code here
    $loop_Until = $loop_Until - 1;
}

Let me explain, provide a slightly better solution, and give you a few alternatives.

If we assume that $i starts out as smaller than $loop_Until, then adding 1 to $loop_Until with the line $loop_Until = $loop_Until + 1; would never make it so that $i is equal or greater than $loop_Until.

You should either subtract from $loop_Until, or add to $i.

Subtracting 1 from a variable can be done quickly by doing, --$variable. Adding 1 to a variable can be done quickly by doing, ++$variable, so you should have:

$loop_Until = 10;

while($i < $loop_Until)
{
    // do some code here
    --$loop_Until;
}

Of course $loop_Until sounds like something you might want to set once, and then have it stay unchanged. In this case, you can set $i and increment that. So first set $i to whatever you want (smaller than $loop_Until, if you want your while loop to run at least once), then:

$loop_Until = 10;

while($i < $loop_Until)
{
    // do some code here
    ++$i;
}

Incidentally, ++$i is faster than $i++

As Lizard mentioned, the for loop is great for doing this. The two equivalent for loops for the two sections of code above are

for($loop_Until = 10; $i < $loop_Until; --$loop_Until)
{
    // do some code here
}

and

for($loop_Until = 10; $i < $loop_Until; ++i)
{
    // do some code here
}

Just make sure you check that your condition will eventually happen with a few numbers on a piece of paper or in your head.

Finally, which of these solutions you pick will depend on whether you want $i or $loop_Until to remain unchanged.

If you have multiple loops, and you want to do all of them the same amount of times, it's probably a good idea to leve $loop_Until untouched, and reset $i at the beginning of each loop.

Answer 4

while( 0 != ($loop_until--) );

Answer 5

Disregard, don't have the time to fiddle with formatting