PHP Control Flow (while)

While

            The  while function is the simplest of all the iterative control statements.  The statement list within a while statement is repeated as long as the condition evaluated has not been met.  The statement list within the while code body can consist of one or more statements.

while (expression) 

{
    -- statements that execute while the expression evaluates false
}

It is a best practice to build error detecting logic into any iterative control statement.  This error control logic should be built in such a way as to detect an infinite loop. In the following example, simple logic has been built into a while function to detect an infinite loop error:




<?php
    $i = 5;
    while ($i < 5) {
        echo '$i <br>';
        $i = $i++;
        if ($i > 20000) { // Break when > 20,000 repititions
            break;
        }
    }
?>

Do ... While

     The do ... while function is based on the while iterative control statement with the difference being the condition is evaluated at the end of the statement execution versus at the beginning.  The statement list within a do ... while function is repeated as long as the condition evaluated has not been met.  The statement list within the do ... while code body can consist of one or more statements.


do {
    -- statements that execute while the expression evaluates false
       and then it iterates through the statements one more time
} while (expression);

A do ... while statement will always be guaranteed to run through the statements contained at least once.  The following example demonstrates how a do ... while statement works:

<?php
    $i = 10;
    do {
        echo $i * $i;
        $i = $i+;
    } while ($i < 5);

/* The number 100 will be displayed, even though 10 is not less than
5. If this was a while statement, the statements would not have run
at all */
?>