(int) / (string) / (array) Cast Since: PHP 4（2000）

// Use a cast operator to convert the type.
(int) $value;
(string) $value;
(float) $value;
(bool) $value;
(array) $value;

// Use settype() to directly change the type of a variable.
settype($var, $type);

<?php
// Convert a string to an integer.
$str = "42";
$num = (int) $str;
echo $num; // Outputs "42".
var_dump($num); // Outputs "int(42)".

// Casting a decimal to an integer truncates the fractional part.
echo (int) 3.9; // Outputs "3".

// Strings that cannot be interpreted as a number become 0.
echo (int) "abc"; // Outputs "0".
echo (int) "123abc"; // The leading numeric part is converted; outputs "123".

// Casting to a string.
echo (string) 100; // Outputs "100".
echo (string) true; // Outputs "1".
echo (string) false; // Outputs an empty string.
echo (string) null; // Outputs an empty string.

// Casting to a boolean.
var_dump((bool) 1); // Outputs "bool(true)".
var_dump((bool) 0); // Outputs "bool(false)".
var_dump((bool) ""); // Outputs "bool(false)".
var_dump((bool) "0"); // Outputs "bool(false)".
var_dump((bool) "abc"); // Outputs "bool(true)".

// Casting to an array.
$val = "Hello";
print_r((array) $val); // Becomes a single-element array.

// Use settype() to change the type of the variable itself.
$price = "1980";
settype($price, "int");
var_dump($price); // Outputs "int(1980)".

// You can also convert using intval(). The second argument specifies the base.
echo intval("0xFF", 16); // Interpreted as hexadecimal; outputs "255".
echo intval("077", 8); // Interpreted as octal; outputs "63".

PHP type casting is a mechanism for explicitly converting a variable to a different type. Values received from forms are always strings, so it is recommended to explicitly cast them with (int) or (float) when using them in numeric calculations. PHP performs automatic type conversion, but relying on implicit conversion can lead to bugs.

A cast operator returns a new converted value and does not modify the original variable. Use settype() if you want to change the type of the variable itself.

Use is_array() / is_string() / is_numeric() to check the type of a variable. For checking whether a variable exists or is empty, isset() / empty() are useful.