Append to beginning of string until length = x

I'm trying to开发者_JAVA百科 write a loop that appends a number to the beginning of a string until it is 15 characters long. What am I missing?

$i = rand(1,9);
while (strlen($fileNameNS > 15)){
    $file13 = $i . $i . $fileNameNS;
}
$i++;

In each iteration of the loop, you modify $file13, but your loop is only looking at $fileNameNS, which never changes! Since it never changes, if the loop condition is initially true, it will always be true, and never exit.

Perhaps you meant this:

$fileNameNS = $i . $i . $fileNameNS;

Your condition is mixed up as well, in two ways.

1. You're continuing while the length is greater than the intended length, when you should be continuing while the length is less than the intended length.
2. You're applying strlen to the comparison $fileNameNS > 15, when you should be applying the comparison to the value of strlen($fileNameNS).

while(strlen($fileNameNS) < 15) {

Note that because you're adding two copies of $i at a time your final length may be 15 or 16. If this isn't what you want, you should be this instead:

$fileNameNS = $i . $fileNameNS;

You incrementing $i with $i++ after the loop is finished, so inside the loop the value of $i will never change. If you mean to increment $i each iteration, so that different digits are prepended each time, you need to move that up one line, inside the loop. However if you do this then $i could end up being longer than one digit, again raising the possibility of the final length being 16.

Already exists a function to do that:

http://php.net/manual/en/function.str-pad.php

As I see on your loop, don't need rand number each time, so str_pad fits well.

Also your while statement is incorrect.

while (strlen($fileNameNS) < 15)

You want it to act while the strlen is less than 15

You also don't need to increment $i outside of the loop. And in fact may want to move your random number generator inside the loop. to have it be a random string of numbers.

for ($i = 0, $str = ''; $i < 15; $i++) {
    $str .= rand(1, 9);
}

$i = rand(1,9);
$file13 = $fileNameNS;
while (strlen($file13) <= 15){
    $file13 = $i . $i . $fileNameNS;
    $i++;
}