PHP Functions: Built-in, String & Numeric Examples

What is a Function in PHP?

A function in PHP is a reusable piece or block of code that performs a specific action. It takes input from the user in the form of parameters, performs certain actions, and gives the output. Functions can either return values when called or simply perform an operation without returning any value.

PHP has over 700 built-in functions that perform different tasks.

Why use Functions?

• Better code organization – PHP functions allow us to group blocks of related code that perform a specific task together.
• Reusability – once defined, a function can be called by a number of scripts in our PHP files. This saves us the time of reinventing the wheel when we want to perform routine tasks such as connecting to the database.
• Easy maintenance – updates to the system only need to be made in one place.

PHP Built in Functions

Built-in functions are predefined functions in PHP that exist in the installation package.

These PHP inbuilt functions are what make PHP a very efficient and productive scripting language.

The built-in functions of PHP can be classified into many categories. Below is a list of the main categories.

String Functions

These are functions that manipulate string data. Refer to the article on strings for implementation examples of string functions.

Numeric Functions

Numeric functions in PHP are the functions that return numeric results.

Numeric PHP functions can be used to format numbers, return constants, perform mathematical computations, and more.

The table below shows the common PHP numeric functions.

<?php
if(is_numeric("guru"))
{
echo "true";
}
else
{
echo "false";
}
?>

<?php
if(is_numeric(123))
{
echo "true";
}
else
{
echo "false";
}
?>

<?php
echo number_format(2509663);
?>

<?php
echo rand();
?>

<?php
echo round(3.49);
?>

<?php
echo sqrt(100);
?>

<?php
echo cos(45);
?>

<?php
echo sin(45);
?>

<?php
echo tan(45);
?>

<?php
echo pi();
?>

Date Function

The date function is used to format a Unix date and time to a human readable format.

Check the article on PHP date functions for more details.

Other functions include:

• Arrays – see the article on arrays for examples
• Files – see the article on files for examples
• Database functions – see the article on MySQL, PHP and other database access methods

Why use User Defined Functions?

User defined functions come in handy when:

• you have routine tasks in your application such as adding data to the database
• performing validation checks on the data
• authenticating users in the system, and similar tasks.

These activities will be spread across a number of pages. Creating a function that all these pages can call is one of the features that make PHP a powerful scripting language.

Before we create our first user defined function, let us look at the rules that we must follow when creating our own functions.

• Function names must start with a letter or an underscore, but not a number
• The function name must be unique
• The function name must not contain spaces
• It is considered good practice to use descriptive function names.
• Functions can optionally accept parameters and return values too.

Let us now create our first function. We will create a very basic function that illustrates the major components of a function in PHP.

<?php

// define a function that adds two numbers

function add_numbers(){
echo 1 + 2;
}
add_numbers ();
?>

Output:

3

HERE,

• “function…(){…}” is the function block that tells PHP that you are defining a custom function
• “add_numbers” is the function name that will be called when using the function.
• “()” can be used to pass parameters to the function.
• “echo 1 + 2;” is the function block of code that is executed. It could be any code other than the one used in the above example.

Let us now look at a fairly complex example that accepts a parameter and displays a message, just like the above function.

Suppose we want to write a function that prints the user name on the screen. We can write a custom function that accepts the user name and displays it on the screen.

The code below shows the implementation.

<?php
function display_name($name)
{
echo "Hello " . $name;
}
display_name("Martin Luther King");
?>

Output:

Hello Martin Luther King

HERE,

• “($name)” is the function parameter called name. The value passed to the function when it is called is displayed after the word Hello.

Let us now look at a function that accepts a parameter and then returns a value. We will create a function that converts kilometers to miles. The kilometers will be passed as a parameter, and the function will return the miles equivalent. The code below shows the implementation.

<?php
function kilometers_to_miles($kilometers = 0)
{
$miles_scale = 0.62;
return $kilometers * $miles_scale;
}
echo kilometers_to_miles(100);
?>

Output:

62

PHP Function Parameters and Return Values

Parameters let a function work on different input each time it runs, and the return statement sends a result back to the caller. PHP offers several ways to control how parameters behave.

• Default values: as in kilometers_to_miles($kilometers = 0), a default is used when the caller omits that argument.
• Pass by reference: prefixing a parameter with & lets the function change the caller’s original variable instead of a copy.
• Return values: return ends the function and hands a value back; without it, the function returns null.

The example below uses a reference parameter and a default rate to add tax to a price in place.

<?php
function addTax(&$price, $rate = 0.1)
{
$price += $price * $rate;
}
$total = 100;
addTax($total);
echo $total;
?>

Output:

110

Because $price is passed by reference, the function updates the original $total variable directly, so the echoed value is 110.

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