PHP DO WHILE Loop

DO .. WHILE is used in PHP to provide a control condition. The idea is to execute a piece of code while a condition is true. The basic syntax of DO .. WHILE is as follows:

DO {
  [code to execute]
} WHILE (conditional statement)

The difference between DO .. WHILE and WHILE is that DO .. WHILE will always execute the [code to execute] at least once, and in a WHILE construct, it is possible for the [code to execute] to never execute.

Let's look at an example. Assuming we have the following piece of code:

$i = 5 DO {   print "value is now " . $i . "<br>";   $i--; } WHILE ($i > 3);

The output of the above code is:

value is now 5 value is now 4

During the 1st iteration, $i = 5, the print statement is executed, $i gets decreased by 1 and becomes 4, then PHP checks the expression, ($i > 3), which turns out to be true. Therefore, the loop continues.

During the 2nd iteration, $i = 4, the print statement is executed, $i gets decreased by 1 and becomes 3, then PHP checks the expression, ($i > 3), which is no longer true. Therefore, PHP exits the loop.

If we change the above code to:

$i = 0 DO {   print "value is now " . $i . "<br>";   $i--; } WHILE ($i > 3);

The output would then be:

value is now 0

Even though the expression ($i > 3) is false from the very beginning, one line is still printed out because in DO .. WHILE, the code in the bracket following DO is always executed at least once.