Booleans and Decisions

In many ways, computer programming is the art of automating decisions. Decisions are made by a computer based on statements that are either true or false. In this section we’ll see how PHP deals with boolean variables and how to made decisions with if and switch statements.

Table of Contents

1. Truthiness and Falsiness
2. Boolean Expressions
3. Really Really Really Equals?
4. If Statements
5. Switch Statements

Truthiness and Falsiness

When working with Boolean expressions PHP contains the constants TRUE and FALSE. However, most other variable types can be coerced into Booleans.

<?php
    function boolean_test($var) {
        if ($var) {
            echo "{$var} is true\n";
        } else {
            echo "{$var} is false\n";
        }
    }
    boolean_test(TRUE);     boolean_test(FALSE);
    boolean_test(0);        boolean_test(1);
    boolean_test(2);        boolean_test(3);
    boolean_test('string'); boolean_test('');
    boolean_test([]);       boolean_test([34]);
    boolean_test(NULL);
?>

Output:

1 is true
 is false
0 is false
1 is true
2 is true
3 is true
string is true
 is false
Array is false
Array is true
 is false

Some things to note here:

• When printing out TRUE we get a 1.
• When print FALSE or NULL a empty string is printer.
• Zero is false while all other numbers are true.
• Empty strings are false, while all other strings are true.
• Empty arrays and hashes are false, while all other arrays and hashes are true.

Resources

• The Nitty-Gritty of Type Comparisons @ PHP.net

Boolean Expressions

A boolean expression is a mathematical expression that results in either true or false.

Boolean expressions can contain the following common operators (and more):

Resources

• George Boole

Really Really Really Equals?

Because PHP will auto-cast your variables when you compare them with different types, the double equals operator doesn’t always act in an expected manner.

For example, the following comparisons will evaluate to true.

42 == "42"
42 == true
0 == false
0 == "a"
"a" == true
0 != true

To avoid these WAT!? moments, use the triple equals operator === when making comparisons.

If Statements

If statements work as expected. Note that elseif is one word when chaining statements.

<?php

if (($wobblypops > 4) || ($wobblypops === 0)) {
    echo 'I pity da fool.';
} elseif ($wobblypops < 4) {
    echo 'Gulp gulp.';
    $wobblypops++;
}

?>

There have been other examples of simple if/else clauses earlier in the notes.

Resources

• if @ PHP.net

Switch Statements

It’s sometimes nice to express long if/else chains as switch statements:

<?php
    $i = 1;
    switch ($i) {
        case 0:
            echo 'i equals 0' . $i;
            break;
        case 1:  // Note: Fall-through
            echo "falling\n";
        case 2:  // Note: Fall-through
            echo "falling\n";
        case 3:
            echo 'i equals 1-3';
            break;
        default:
            echo 'Nothing special about the default.';
    }
?>

Note the “fall-through” cases for 1 and 2. Execution does not stop until we reach a break or the end of the switch block.

Output:

falling
falling
i equals 1-3

Strings can also be used as the target of a switch:

<?php
    switch($beer)
    {
        case 'trad':
        case 'fort garry dark':
        case 'hoegaarden':
            echo 'Good choice';
            break;
        default:
            echo 'Please make a new selection...';
    }
?>

Resources

• Switch @ PHP.net