Using strtoupper() in PHP to Convert Strings to Uppercase

In PHP, the strtoupper() function is commonly used to convert all alphabetic characters in a string to uppercase.

Basic Syntax of strtoupper()

strtoupper(string $string): string

Parameter Description

$string

: The string to be converted.

Return Value

The function returns the uppercase version of the input string.

Example 1

$str = "Hello World!";  // define a string variable
$result = strtoupper($str);  // convert to uppercase
echo $result;  // outputs: HELLO WORLD!

This example defines a string variable $str with the value "Hello World!", calls strtoupper() to convert it, stores the result in $result, and outputs the uppercase string.

Example 2

$str = "this is a sentence.";  // define a multi‑word string
$result = strtoupper($str);  // convert to uppercase
echo $result;  // outputs: THIS IS A SENTENCE.

The second example shows that the function works with strings containing multiple words, converting all lowercase letters to uppercase while leaving spaces unchanged.

Example 3

$str = "123ABC!@#";  // string with numbers and special characters
$result = strtoupper($str);  // convert to uppercase
echo $result;  // outputs: 123ABC!@#

This example demonstrates that strtoupper() only affects alphabetic characters; numbers and special symbols remain unchanged.

Overall, strtoupper() provides a simple way to transform lowercase letters to uppercase in PHP strings, while leaving non‑alphabetic characters untouched.