ZetCode

Type Conversions in PHP

last modified June 3, 2025

In the article we explore PHP's type conversion system, covering automatic conversions, explicit casting, and commonly used conversion functions.

PHP is a dynamically typed language, meaning variables do not have fixed types. It automatically converts values between types as needed, a process known as type juggling.

Since PHP determines a variable's type based on its assigned value, it offers great flexibility. However, this dynamic behavior can sometimes lead to unexpected results if types are not carefully managed. For instance, a variable can hold a string initially and later be assigned an integer without causing errors. While convenient, this can create issues in scenarios where a variable's type is critical, such as arithmetic operations or comparisons.

PHP Type Conversion Overview

PHP supports several types: integers, floats, strings, booleans, arrays, and objects. Type conversion allows you to convert between these types as needed.

Conversion Type Description Example
Type Juggling Automatic conversion in expressions $sum = "5" + 2; // int(7)
Type Casting Explicit conversion using casting $int = (int) "123";
settype() Change variable's type settype($var, "float");
Conversion Functions Specialized conversion functions $num = intval("42");

The table summarizes the main ways to convert types in PHP. Type juggling occurs automatically in expressions, while type casting allows explicit conversion. The settype() function changes a variable's type, and conversion functions like intval() provide specialized conversions.

Type Juggling (Automatic Conversion)

PHP automatically converts types in expressions based on context. This is called type juggling.

type_juggling.php 
<?php

// String to number conversion
$sum = "10" + 5;  // int(15)
echo gettype($sum) . ": " . $sum . "\n";

// Boolean conversion
$result = "hello" == true;  // bool(true)
var_dump($result);

// String concatenation
$concat = 5 . " items";  // string(7) "5 items"
echo $concat . "\n";

// Float to int in array key
$arr = [3.5 => "value"];
echo array_key_first($arr);  // int(3)

PHP automatically converts types in these common situations: 

$ php type_juggling.php
integer: 15
bool(true)
5 items
3

Explicit Type Casting

PHP provides several ways to explicitly convert between types using casting operators.

casting.php 
<?php

// String to integer
$int = (int) "123";
echo "int: " . $int . "\n";

// Float to integer (truncates)
$truncated = (int) 3.99;
echo "truncated: " . $truncated . "\n";

// Integer to boolean
$bool = (bool) 1;
var_dump($bool);

// Array to string
$str = (string) [1, 2];
echo "array as string: " . $str . "\n";

// Available cast types:
// (int), (integer) - to integer
// (bool), (boolean) - to boolean
// (float), (double), (real) - to float
// (string) - to string
// (array) - to array
// (object) - to object
// (unset) - to NULL (deprecated)

Casting is useful when you need to ensure a specific type for a variable or function parameter. Note that some casts like array-to-string produce standardized results ("Array") rather than converting the content. 

$ php casting.php
int: 123
truncated: 3
bool(true)
array as string: Array

Conversion Functions

PHP provides specialized functions for type conversion with additional control.

conversion_functions.php 
<?php

// String to number conversion
$num = intval("42 items");  // 42
$float = floatval("3.14");  // 3.14

// Base conversion
$hex = hexdec("FF");  // 255
$bin = bindec("1010"); // 10

// Type setting
$var = "123.45";
settype($var, "float");

// String representation
$str = strval(123);

echo "intval: " . $num . "\n";
echo "hexdec: " . $hex . "\n";
echo "settype: " . gettype($var) . "\n";

These functions provide more control than simple casting: 

$ php conversion_functions.php
intval: 42
hexdec: 255
settype: double

String to Number Conversion

PHP can convert strings to numbers automatically in arithmetic operations, or you can use explicit casting and functions like intval and floatval for more control. This is useful when parsing user input or working with data from external sources.

string_to_number.php 
<?php

// Automatic in arithmetic
$sum = "10" + 5;  // 15

// Explicit with casting
$num = (int) "123";

// Using intval() with base
$hex = intval("FF", 16);  // 255

// Float conversion
$price = floatval("19.99");

echo "sum: $sum, num: $num, hex: $hex, price: $price\n";

Number to String Conversion

Numbers can be converted to strings automatically during concatenation, or explicitly using casting or formatting functions like sprintf. This is helpful for displaying numbers in output or building dynamic strings.

number_to_string.php 
<?php

// Automatic in concatenation
$str = "Value: " . 42;

// Explicit casting
$strNum = (string) 123;

// Formatted conversion
$formatted = sprintf("%.2f", 3.14159);

echo "$str\n$strNum\n$formatted\n";

Boolean Conversion Rules

PHP has specific rules for converting values to boolean. Values like false, 0, 0.0, "", "0", empty arrays, and null are considered false; all other values are true. Understanding these rules is important for writing correct conditional logic.

boolean_conversion.php 
<?php

// Values that evaluate to false:
// false, 0, 0.0, "", "0", [], null

$trueValues = [1, "hello", [1], true];
$falseValues = [0, "", null, []];

foreach ($trueValues as $val) {
    echo "$val is " . ($val ? "true" : "false") . "\n";
}

The above code demonstrates how different values evaluate to true or false in PHP. This is crucial for understanding how conditions work in control structures like if statements.

Type Checking Functions

Type checking functions help you verify a variable's type before performing conversions or operations. This can prevent errors and make your code more robust, especially when handling user input or dynamic data.

Function Description Example
is_int Check if integer is_int(42)
is_float Check if float is_float(3.14)
is_numeric Check if number or numeric string is_numeric("123")
is_string Check if string is_string("text")
is_array Check if array is_array([])
is_bool Check if boolean is_bool(true)

The above functions allow you to check a variable's type before performing operations or conversions. This is especially useful when dealing with user input or data from external sources, where types may not be guaranteed.

Strict Type Comparisons

For strict type checking, use === instead of ==:

strict_comparison.php 
<?php

// Loose comparison (type juggling)
if (0 == "0") {  // true
    echo "Loose match\n";
}

// Strict comparison (type and value)
if (0 === "0") {  // false
    echo "This won't print\n";
} else {
    echo "Strict mismatch\n";
}

The === operator checks both value and type, while == performs type juggling before comparison.

Source

PHP Manual: Type Juggling
PHP Manual: Type Conversion

Understanding PHP's type conversion system is essential for writing robust code. While type juggling is convenient, being explicit with casting and strict comparisons can prevent subtle bugs.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

List all PHP tutorials.