Learning PHP, MySQL, JavaScript, and CSS, 2nd Edition

Looping

One of the great things about computers is that they can repeat calculating tasks quickly and tirelessly. Often you may want a program to repeat the same sequence of code again and again until something happens, such as a user inputting a value or reaching a natural end. PHP’s various loop structures provide the perfect way to do this.

To picture how this works, take a look at Figure 4-4. It is much the same as the highway metaphor used to illustrate if statements, except that the detour also has a loop section that—once a vehicle has entered—can be exited only under the right program conditions.

Figure 4-4. Imagining a loop as part of a program highway layout

while Loops

Let’s turn the digital car dashboard in Example 4-26 into a loop that continuously checks the fuel level as you drive using a while loop (Example 4-28).

Example 4-28. A while loop

<?php
$fuel = 10;

while ($fuel > 1)
{
    // Keep driving ...
    echo "There's enough fuel";
}
?>

Actually, you might prefer to keep a green light lit rather than output text, but the point is that whatever positive indication you wish to make about the level of fuel is placed inside the while loop. By the way, if you try this example for yourself, note that it will keep printing the string until you click the Stop button in your browser.

Note

As with if statements, you will notice that curly braces are required to hold the statements inside the ...