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. This article introduces the function, its syntax, parameters, and return value, and provides several practical code examples.

The basic syntax is:

strtoupper(string $string): string

Parameter:

$string : The input string to be converted.

Return value: The uppercase version of the input string.

Example 1 – Simple string:

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

This example shows a basic conversion of a single phrase.

Example 2 – Multi‑word sentence:

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

Here the function handles a string containing several words.

Example 3 – String with numbers and special characters:

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

Since strtoupper() only affects alphabetic characters, digits and symbols remain unchanged.

In summary, strtoupper() provides a straightforward way to transform lowercase letters to uppercase in PHP strings, requiring only the string as an argument and returning the transformed result; non‑alphabetic characters are left untouched.