Booleans

A boolean has only two possible values: true or false. Booleans are the answer to a yes-or-no question, and they drive every decision in your code.

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<?php
$isLoggedIn = true;
$hasPaid = false;

var_dump($isLoggedIn, $hasPaid);

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bool(true)
bool(false)

Comparisons produce booleans

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<?php
$age = 20;

var_dump($age >= 18);
var_dump($age === 30);

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bool(true)
bool(false)

Printing a boolean

echo true prints 1, and echo false prints nothing at all. That surprises many beginners.

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<?php
echo "[" . true . "]\n";
echo "[" . false . "]";

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[1]
[]

To see the real value, use var_dump(), or write your own words.

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<?php
$active = false;
echo $active ? "Active" : "Inactive";

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Inactive

What counts as false?

When PHP needs a yes or no (for example in an if), it converts the value to a boolean. These values become false, and everything else becomes true:

• false
• 0 and 0.0
• "" (empty string) and "0"
• [] (empty array)
• null

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<?php
var_dump((bool) "hello");
var_dump((bool) "0");
var_dump((bool) []);
var_dump((bool) "false");

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bool(true)
bool(false)
bool(false)
bool(true)

Notice the last line: the text "false" is a non-empty string, so it is true.