PHP strtolower Function Explained

The strtolower function is a built-in PHP function that converts all characters in a string to lowercase. Here is its syntax:

string strtolower ( string $string )

$string is the string that needs to be converted to lowercase.

原文：我不知道该怎么解决这个问题。

Option: I don’t know how to solve this problem.

$str = "Hello World!";
echo strtolower($str); // 输出 "hello world!"