7. PHP Data Types

What you will learn

The main PHP data types
How to check and convert types
What null means
How truthy and falsy values behave

The types

Type	Example	Meaning
string	`"Hello"`	Text
int	`42`	Whole number
float	`3.14`	Decimal number
bool	`true`, `false`	Yes or no
array	`[1, 2, 3]`	A list or map of values
object	an instance of a class	Data with behaviour
null	`null`	No value

Unlike JavaScript, PHP separates whole numbers (int) from decimals (float).

Checking a type

gettype() returns the type name, and var_dump() shows type and value.

PHP code

<?php
echo gettype("Hi") . "<br>";
echo gettype(42) . "<br>";
echo gettype(3.14) . "<br>";
echo gettype(true) . "<br>";
echo gettype([1, 2]) . "<br>";
echo gettype(null);

What the browser shows

string
integer
double
boolean
array
NULL

gettype() uses older names: integer, double (for float), and boolean. Tests such as is_int(), is_float(), is_string(), is_bool(), is_array(), and is_null() return true or false.

Numbers

PHP code

<?php
var_dump(10);
var_dump(10.5);
var_dump(10 / 4);
var_dump(10 / 5);
var_dump(intdiv(10, 4));

What you should see (inside <pre>)

int(10)
float(10.5)
float(2.5)
int(2)
int(2)

Division gives an int when the result is exact, and a float otherwise. intdiv() always gives a whole-number quotient.

Booleans and truthiness

In a condition, these values count as false: false, 0, 0.0, "" (empty string), "0", [] (empty array), and null. Everything else is true.

PHP code

<?php
$tests = ["", "0", "0.0", "hello", 0, [], [0]];

foreach ($tests as $value) {
    echo var_export($value, true) . " is " . ($value ? "true" : "false") . "<br>";
}

What the browser shows

” is false
‘0’ is false
‘0.0’ is true
‘hello’ is true
0 is false
array (
) is false
array (
0 => 0,
) is true

Note that "0.0" is true, but "0" is false. This is a PHP quirk. When it matters, compare explicitly instead of relying on truthiness.

null

null means “no value”. A variable is null if you assign it, if it was never set, or after unset().

PHP code

<?php
$x = null;

echo is_null($x) ? "x is null. " : "x has a value. ";
echo isset($x) ? "isset: yes" : "isset: no";

Output

x is null. isset: no

isset() returns false for null as well as for undefined variables.

Type conversion (casting)

PHP converts types automatically in some situations (called type juggling). You can also convert on purpose with a cast in brackets.

PHP code

<?php
$text = "25";

var_dump((int) $text + 5);
var_dump((float) "3.7");
var_dump((string) 99);
var_dump((bool) "hello");
var_dump((int) "abc");
var_dump((int) 7.9);

What you should see (inside <pre>)

int(30)
float(3.7)
string(2) "99"
bool(true)
int(0)
int(7)

Casting a decimal to int cuts off the decimal part without rounding. Casting non-numeric text to int gives 0. Use round() when you want rounding.

Strict comparison

== converts types first, === does not. As in JavaScript, prefer ===.

PHP code

<?php
var_dump(5 == "5");
var_dump(5 === "5");
var_dump(0 == "abc");
var_dump(0 === "abc");

What you should see (inside <pre>)

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

Version note: in PHP 8, 0 == "abc" is false. In PHP 7 and earlier it was true, which caused real bugs. This is another reason to use === and a current PHP version.

Everything that arrives from a form or the address bar is a string, even if it looks like a number. Convert and check it before using it in calculations.

Common mistakes

Using == and being surprised by automatic conversion.
Assuming "0.0" is false.
Casting text to a number without checking it was a number.
Forgetting that float arithmetic can be slightly inexact, such as 0.1 + 0.2.
Trusting form data to be the type you expect.

Exercise

$qty = "3"; and $price = "4.5"; arrive as text. Convert them and print the total with two decimals, using number_format().

Show solution

<?php
$qty = "3";
$price = "4.5";

$total = (int) $qty * (float) $price;
echo number_format($total, 2);

The output is 13.50.

Knowledge check

1. Which two PHP types hold numbers?

int and float.

2. What does (int) "abc" give?

0

3. Which comparison operator checks type as well as value?

===

Summary

Main types: string, int, float, bool, array, object, and null.
Check with gettype() and var_dump(), and convert with casts.
Use ===, remember the falsy values, and treat outside data as text.