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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 can simply perform an operation without returning any value.
PHP has over 700 functions built in that perform different tasks.
In this tutorial, you will learn-
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 time of reinventing the wheel when we want to perform some 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 FunctionsBuilt 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 the list of the categories.
String FunctionsThese 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 function can be used to format numbers, return constants, perform mathematical computations etc.
The table below shows the common PHP numeric functions
Function
Description
Example
Output
is_number
Accepts an argument and returns true if its numeric and false if it’s not
<?php if(is_numeric("guru")) { echo "true"; } else { echo "false"; } false <?php if(is_numeric (123)) { echo "true"; } else { echo "false"; } true number_format Used to formats a numeric value using digit separators and decimal points <?php echo number_format(2509663); 2,509,663 rand Used to generate a random number. <?php echo rand(); Random number round Round off a number with decimal points to the nearest whole number. <?php echo round(3.49); 3 sqrt Returns the square root of a number <?php echo sqrt(100); 10 cos Returns the cosine <?php echo cos(45); 0.52532198881773 sin Returns the sine <?php echo sin(45); 0.85090352453412 tan Returns the tangent <?php echo tan(45); 1.6197751905439 pi Constant that returns the value of PI <?php echo pi(); 3.1415926535898Date Function
The date function is used to format Unix date and time to human readable format.
Check the article on PHP date functions for more details.
Other functions
These include;
Arrays – see the article on
arrays
for examplesFiles – see the article on
files
for examplesDatabase functions – see the article on MySQL PHP and other database access methods v2
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 etc.
These activities will be spread across a number of pages.
Creating a function that all these pages can be calling is one of the features that make PHP a powerful scripting language.
Before we create our first user defined function, let’s 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 a good practice to use descriptive function names.
Functions can optionally accept parameters and return values too.
Let’s now create our first function. We will create a very basic function that illustrates the major components of a function in PHP.
<?php function add_numbers(){ echo 1 + 2; } add_numbers ();Output:
3HERE,
“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 ‘Hello function!’;” is the function block of code that is executed. It could be any code other than the one used in the above example.
Let’s now look at a fairly complex example that accepts a parameter and display 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 " . $name; } display_name("Martin Luther King");Output:
Hello Martin Luther KingHERE,
“…($name){…” is the function parameter called name and is initialized to nameless. If no parameter is passed to the function, nameless will be displayed as the name. This comes in handy if not supplying any parameter to the function can result in unexpected errors.
Let’s 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. The function will return the miles equivalent to the passed kilometers. 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 Summary
Define function in PHP: Function is a block of code that performs specific task.
Built in function in PHP is a function that is shipped with PHP
PHP has over 700 built in functions
String functions manipulate string data
Numeric functions manipulate numeric data
Date functions manipulate date data
Other functions such as is_array, fopen etc. are used to manipulate arrays and files respectively
User defined functions are functions that you can create yourself to enhance PHP
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