What are the potential pitfalls of using global variables and the define() function in PHP programming?

Using global variables can make code harder to maintain and debug, as they can be accessed and modified from anywhere in the codebase. This can lead to unintended side effects and make it difficult to track down bugs. Similarly, using the define() function to create constants can also lead to issues if the constants are not used consistently throughout the code. To solve this issue, it's recommended to avoid using global variables whenever possible and instead pass variables as parameters to functions. For constants, consider using class constants or defining constants within a specific scope to prevent conflicts.

// Avoid using global variables
function myFunction($param) {
    // do something with $param
}

$myVar = 'value';
myFunction($myVar);

// Use class constants
class MyClass {
    const MY_CONSTANT = 'constant value';

    public function myMethod() {
        echo self::MY_CONSTANT;
    }
}

$myClass = new MyClass();
$myClass->myMethod();