PHP Functions: Classifications, Parameters and More

PHP Functions are blocks of reusable code that are designed to perform a specific task. Understand its Classifications, Arguments & default values with simple examples:

In this tutorial, you will learn what a PHP function is, built-in functions (such as PHP empty(), count(), etc.), user-defined functions, parameters, arguments & default values, returning values, recursive & anonymous PHP functions, and frequently asked questions (FAQs).

Please note that we have used PHP version 7 in all examples.

Let’s begin!

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PHP Functions: Guide with Examples

What is a PHP Function

A PHP function is a piece of reusable code. It may take input as an argument (or parameter) and return a value after some processing. You may have already seen some functions in our previous tutorials, as they are widely used.

The following piece of code shows the syntax of a function.

<?php
 
function funcName(){  

//executable code

}  

?>

A function name must start with a letter or an underscore symbol, and it cannot start with a number or any other symbol.

Let’s consider the following example. What would you expect after running this code?

<?php  

function saySomething(){  
	echo "Hello World!";  
}  

?>

Hello World! as output?

No, nothing will display. To get an output onto your browser (screen), you need to call the function. Otherwise, even if the function is working properly, it will not produce any output to the user.

Now, see the modified example below. We need to call the function just outside the function, and not inside it.

You can practice this example by running the following programming code:

<?php  

function saySomething(){  

	echo "Hello World!";  
	
}  

saySomething(); //calling the function  

?>

Output:

Hello World!

Some of the advantages of using functions are less code needed, code reusability, easy-to-understand and maintain code, and easy error detection.

Classification of Functions

There are two major types of PHP functions. They are:

1. Built-in functions
2. User-defined functions

Built-in Functions

There are over 1000 built-in functions in PHP. Due to the space limit, we have only shown some frequently used ones in the list below.

• array_key_exists()
• array_keys()
• array_map()
• array_merge()
• class_exists()
• count()
• date()
• dirname()
• empty()
• explode()
• file_exists()
• file_get_contents()
• get_class()
• implode()
• in_array()
• is_array()
• is_null()
• is_object()
• is_string()
• json_encode()
• preg_match()
• preg_replace()
• sprintf()
• str_replace()
• strlen()
• strpos()
• strtolower()
• substr()
• time()
• trim()

Let’s see a couple of examples. You can practice these examples by running the following programming code.

Example 1: count() – It counts the total number of elements in an array.

<?php
	
	$fruits = array('apple','mango','banana');
	echo count($fruits);	
	
?>

Output:

3

Example 2: date() – It formats a local time/date.

<?php
	
	echo date('l jS \of F Y');
	
?>

Output:

Wednesday 21st of July 2021

Note: It will display the current date in the given format. Also, note that you can customize this format.

User-defined Functions

The user (developer or programmer) can create their functions. They are called user-defined functions.

Let’s see an example. You can practice this example by running the following programming code:

<?php  

function displayName(){  

	echo "Hi, Jane Doe!";  
	
}  

displayName(); //calling the function  

?>

Output:

 Hi, Jane Doe!

Parameters, Arguments, and Default Values

Even though parameters and arguments look similar, they are not the same.

A parameter is a variable defined by a function. It gets a value when the function is called. A function can take one parameter or several parameters separated by a comma.

On the other hand, an argument is a value that is passed to a function.

Let’s see some examples. You can practice these examples by running the following programming code:

Example 1:

<?php  

	function myFunc1($x,$y) { 
	
		$z=$x + $y;
		
		echo $z."<br/>";
		
	}  

	myFunc1(10,20); 
	
?>  

Output:

30

In the above example, parameters are $x and $y. Arguments are 10 and 20.

Example 2:

<?php  

	function myFunc2($x=100,$y=200) {  

		$z=$x + $y;
		
		echo $z;
		
	}  
	
	myFunc2(); 
	
?>  

Output:

300

Variables can be arguments. In the above example, myFunc2 takes two arguments, $x and $y (not 100 and 200).

Example 3:

<?php  

function sayHi($name){  

	echo "Hi $name<br/>"; 
 
}  

sayHi("Alex");  
sayHi("David");  
sayHi("John");  

?>

Output:

Hi Alex
Hi David
Hi John

Example 4:

<?php  

function getInfo($name,$age){  

	echo "$name is $age years old.<br/>"; 
 
}  

getInfo("Alex", 18);  
getInfo("David", 21);  
getInfo("John", 19);  

?>

Output:

Alex is 18 years old.
David is 21 years old.
John is 19 years old.

Example 5:

<?php  

function getInfo($name,$age=19){  

	echo "$name is $age years old.<br/>"; 
 
}  

getInfo("Alex", 18);  
getInfo("David", 21);  
getInfo("John");  

?>

Output:

Alex is 18 years old.
David is 21 years old.
John is 19 years old.

In this example, we didn’t specifically pass the age of John when calling the function. Therefore, it has taken the value of age as 19. In other words, the value 19 acts as the default value for $age.

Passing Arguments by Reference

Usually, arguments are passed by value. In addition, we can pass the arguments by reference too. The & operator is used to indicate arguments passed by reference.

Let’s see an example. You can practice this example by running the following programming code:

<?php
 
	function addition(&$val) {
	  $val += 20;
	}

	$num = 5;
	addition($num);
	echo $num;

?>

Output:

25

Returning Values

Functions can return values. It uses the return keyword to return values.

Let’s see an example. You can practice this example by running the following programming code:

<?php

function mySum($num1, $num2, $num3){
    $sum = $num1 + $num2 + $num3;
    return $sum."<br/>";
}
 
echo mySum(1, 2, 3); // sum of 1+2+3 which is 6
echo mySum(10, 10, 20); // sum of 10+10+20 which is 40

?>

Output:

6

40

PHP Recursive Functions

Functions that call themselves are known as recursive functions.

Let’s see an example. You can practice this example by running the following programming code:

<?php    

function printNum($num) {    
    if($num<=5){    
		echo "$num <br/>";    
		printNum($num+1);    
    }  
}    
printNum(1);  
  
?>  

Output:

1 
2 
3 
4 
5

Note: For a better understanding of the above example, you need to know about PHP if statements.

PHP Anonymous Functions

Anonymous functions are functions that have no names.

Let’s see an example. You can practice this example by running the following programming code:

<?php
 
	$var = function() {
		
		echo "I Am Anonymous.";
	};

	$var();

?>

Output:

I Am Anonymous.

Frequently Asked Questions

Conclusion

A function is a block of code that can be reused.

It can take input as arguments and return values. There are over 1000 built-in functions available in PHP, and you can also build your functions.

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