CODEWITHSUNDEEP
phpwhile-loop
Keith
Keith

Reputation: 26489

Possible to use a while loop within a loop?

What I am trying to do is the following: I have an array of values, these values will eventually be used to generate a random unique string but that's a little later. First I would like to loop through all the values in the array (foreach loop) then I would like to limit this (while loop) Is this a correct method for doing this?

The below code does not work, can anybody see what I'm doing wrong?

<?php 

    $array = array(
          '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', 
          'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 
          'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 
          'u', 'v', 'w', 'x', 'y', 'z', '!', '£', '$', '%',
          '^', '&', '*', '(', ')', '_', '+', '{', '}'
    );

    $length_of_unique_key = 15;
    $counter = 0;

    foreach($array as $values)
    {
          $counter++;

          while ($counter <= $length_of_unique_key)
          {

          }
    }

?>

Upvotes: 0

Views: 2880

Answers (4)

bsneeze
bsneeze

Reputation: 4479

Shouldn't you be incrementing your counter within the while loop, so it can exit?

Upvotes: 11

Calvin
Calvin

Reputation: 4619

The best way to see what is wrong with a loop (or any other control structure) is just to run through it. Sometimes you can do it in your head; at other times, it might be helpful to insert trace points into your code.

In this case, I think if you simply run through the code in your head, you'll be able to pick up what's wrong with it. But for didactic purposes, I'll run through it here. First let's number each line of code:

$array = array(...);               // line 1
$length = 15;                      // line 2
$counter = 0;                      // line 3
foreach($array as $values)         // line 4
{
      $counter++;                  // line 5
      while ($counter <= $length)  // line 6
      {
                                   // line 7
      }                            // line 8
                                   // line 9
}                                  // line 10

Now let's run through it:

  1. $array is assigned a single dimensional array:
    array(0 => '1', 1 => '2', 2 => '3', ...)
  2. $length is set to 15.
  3. $counter is to set 0.
  4. Begin for loop; $values = $array[0] = '1'.
  5. $counter is incremented. $counter = 1.
  6. Begin while loop; check that $counter (1) <= $length (15).
  7. Do nothing.
  8. Go back to line 6.
  9. Line 6: If $counter (1) <= $length (15), continue loop.
  10. Line 7: Do nothing.
  11. Line 8: Go back to line 6.
  12. Line 6: $counter (1) is still <= $length (15), go into loop again.
  13. Line 7: Do nothing.
  14. Line 8: Go back to line 6.

As you can see, you are stuck in an infinite loop because neither $counter nor $length change values. So the while condition in line 6 always evaluates to true (1 <= 15).

Upvotes: 7

Sam Becker
Sam Becker

Reputation: 19636

Why not do something like the below code, it generates a key with one loop. Hell, why not make a function for generating keys?

function keyval($length)
{
    $length_of_unique_key = $length;
    $array = array(
          '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', 
          'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 
          'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 
          'u', 'v', 'w', 'x', 'y', 'z', '!', '£', '$', '%',
          '^', '&', '*', '(', ')', '_', '+', '{', '}'
    );
    for($i=0;$i<$length_of_unique_key;$i++)
    {
        $key.=$array[rand(0,sizeof($array)-1)];
    }
    return $key;
}

echo keyval(15);

Upvotes: 0

Scott Evernden
Scott Evernden

Reputation: 39950

All the code you've posted is legit, but clearly you have left something out and that's the part that's going to help answering this... Otherwise, your $counter stays constant during the while loop and it'll never exit

Upvotes: 0

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