(PHP 4, PHP 5, PHP 7)
  do-while loops are very similar to
  while loops, except the truth expression is
  checked at the end of each iteration instead of in the beginning.
  The main difference from regular while loops is
  that the first iteration of a do-while loop is
  guaranteed to run (the truth expression is only checked at the end
  of the iteration), whereas it may not necessarily run with a
  regular while loop (the truth expression is
  checked at the beginning of each iteration, if it evaluates to
  FALSE right from the beginning, the loop
  execution would end immediately).
 
There is just one syntax for do-while loops:
<?php
$i = 0;
do {
    echo $i;
} while ($i > 0);
?>
   The above loop would run one time exactly, since after the first
   iteration, when truth expression is checked, it evaluates to
   FALSE ($i is not bigger than 0) and the loop
   execution ends.
 
Advanced C users may be familiar with a different usage of the do-while loop, to allow stopping execution in the middle of code blocks, by encapsulating them with do-while (0), and using the break statement. The following code fragment demonstrates this:
<?php
do {
    if ($i < 5) {
        echo "i is not big enough";
        break;
    }
    $i *= $factor;
    if ($i < $minimum_limit) {
        break;
    }
   echo "i is ok";
    /* process i */
} while (0);
?>
Don't worry if you don't understand this right away or at all. You can code scripts and even powerful scripts without using this 'feature'. Since PHP 5.3.0, it is possible to use goto operator instead of this hack.