while loop inside another while loop only runs one time

Question

Hi I'm fairly new to coding and brand new to the stackoverflow community, so bear with me.

I'm trying to make a code that will create the following output:

a0

b0 b1 b2 a1

b0 b1 b2 a2

b0 b1 b2

with this code:

    <?php
    $count1 = 0;
    $count2 = 0;
    while ($count1 < 3){
       echo "a".$count1."<br>";
       while ($count2 < 3){
          echo "b".$count2." ";
          $count2 ++;
          }
       $count1++;
       } 
    ?>

My problem is that the nested while loop only runs one time and gives me:

a0

b0 b1 b2 a1

a2

The output I want might be achieved by using a for loop or some other method instead, but I'm curious why this doesn't work. It's also an early stage of a code that should run through a database query for which I have only seen examples with while loops.

Thanks it advance.

After 1 time through the inner loop `$count2` is `3`, so the 2nd/3rd time through the outer loop `(3 < 3)` is false. If you want it to run again, you need to reset `$count2`. — Sean, Sep 14 '14 at 00:17

score 3 · Accepted Answer · answered Sep 14 '14 at 00:20

You need to reset the counter. You don't need to define the variable outside of the whiles, just do it in the first one.

$count1 = 0;
while ($count1 < 3){
    echo "a".$count1."<br>";
    $count2 = 0;
    while ($count2 < 3){
        echo "b".$count2." ";
        $count2 ++;
    }
    $count1++;
}

score 1 · Answer 2 · edited Sep 14 '14 at 00:24

You need to reset the count2 each time you loop over count1.

Like so:

<?php
$count1 = 0;
$count2 = 0;
while ($count1 < 3){
    echo "a".$count1."<br>";
    while ($count2 < 3){
        echo "b".$count2." ";
        $count2 ++;
    }
    $count2 = 0;
    $count1++;
}
?>

You can also do a for loop.

for ($count1 = 0; $count1 < 3; $count1 ++) {
    echo "a".$count1."<br>";
    for ($count2 = 0; $count2 < 3; $count2 ++) {
        echo "b".$count2." ";
    }
}

score 1 · Answer 3 · answered Sep 14 '14 at 00:18

You need to "reset" the value of $count2 between each time the outter loop runs. Note the $count2 = 0:

<?php
$count1 = 0;
$count2 = 0;
while ($count1 < 3){
   echo "a".$count1."<br>";
   while ($count2 < 3){
      echo "b".$count2." ";
      $count2 ++;
      }
   $count1++;
   $count2 = 0;
   } 
?>

while loop inside another while loop only runs one time

3 Answers3