PHP has another data type called “boolean”. A boolean is not a string or a number and it can only be either true or false. When we say true, we’re not referring to the string 'true' or even the number 1.

The true and false boolean values can also be written as TRUE or FALSE, either way it’s best to choose one and stick to it.

Booleans are commonly used in PHP when performing tests, for example:

echo is_int(4); // Outputs: 1
echo is_float(4); // Outputs: 

echo is_int(4.4); // Outputs: 
echo is_float(4.4); // Outputs: 1

echo is_string(2); // Outputs: 
echo is_string('2'); // Outputs: 1

Take note that in PHP, the output of a true value is the number 1 whereas the output of a false value is nothing (as you can see in the example code above).

There’s a built-in PHP function called is_bool to check if something is a boolean or not like so:

echo is_bool('Hello World'); // Outputs: 
echo is_bool(1); // Outputs: 
echo is_bool(true); // Outputs: 1
echo is_bool(false); // Outputs: 1

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This is part 11 of the PHP Basics series.