How to define and call functions?

In PHP, defining and calling functions is a fundamental part of programming. Functions help you encapsulate reusable pieces of code and make your scripts more organized and efficient. Here’s how you can define and call functions in PHP:

Defining Functions:

1. Function Declaration: To define a function, you use the `function` keyword followed by the function name, a pair of parentheses `()`, and a pair of curly braces `{}` to enclose the function’s code. For example:

```php
function greet() {
    echo "Hello, World!";
}
```

2. Parameters: You can specify parameters within the parentheses to allow the function to accept input values. Parameters are variables that hold the data passed into the function. For instance:

```php
function greetWithName($name) {
    echo "Hello, " . $name . "!";
}
```

Calling Functions:

1. Function Invocation: To execute a function, you simply use its name followed by parentheses, optionally passing arguments if the function expects them. For example:

```php
greet(); // Calling the 'greet' function without arguments
greetWithName("John"); // Calling the 'greetWithName' function with an argument
```

2. Passing Arguments: When calling a function with parameters, you pass values that match the parameter names. The function then uses these values within its code. Here’s how you call a function with arguments:

```php
greetWithName("Alice"); // Output: Hello, Alice!
```

3. Return Values: Functions can return values using the `return` statement. This allows you to get results from a function’s execution. For example:

```php
function add($a, $b) {
    return $a + $b;
}

$result = add(5, 3); // $result now holds the value 8
```

Defining and calling functions in PHP is a fundamental concept. It involves declaring functions with `function` keyword, specifying parameters if needed, and then invoking the functions by using their names along with any necessary arguments. Functions help modularize code, promote reusability, and make your PHP scripts more organized and maintainable.