In PHP, strtolower() is a built-in function that converts a string to lowercase. It's useful when you want to ensure consistency, especially in cases like comparing strings (e.g., user inputs, email addresses, etc.) where letter casing might differ.

Syntax:

strtolower(string $string): string

• Parameter: A string you want to convert to lowercase.
• Returns: The lowercase version of the string.

Example 1: Basic usage

$text = "HeLLo WoRLD!";
$lowercaseText = strtolower($text);

echo $lowercaseText;
// Output: hello world!

Example 2: Email normalization

$userEmail = "John.DOE@Example.com";
$normalizedEmail = strtolower($userEmail);

echo $normalizedEmail;
// Output: john.doe@example.com

Example 3: Case-insensitive comparison

$userInput = "Admin";
$expectedRole = "admin";

if (strtolower($userInput) === $expectedRole) {
    echo "Access granted.";
} else {
    echo "Access denied.";
}
// Output: Access granted.

Notes:

• strtolower() only works with standard ASCII characters. For multibyte (Unicode) strings (like accented characters), use mb_strtolower() instead:

  mb_strtolower("MÜNCHEN", "UTF-8"); // Outputs: münchen