This tutorial is intended to be a simple easy to understand introduction to the custom functions php allows you to create.

Please note: This function is not intended to be useful nor should it be used. It is solely for learning purposes.

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<?php
	$var = 'Hello Im a variable.';
 
	function makeBold( $text ) //The variable inside our makeBold fucntion $text, does not have to be a variable called
				   //$text when we run the function. It is just showing you where a variable or string should
				   //go so that it can be used inside the function.
	{
		$var = '<b>' . $text . '</b>';
		//Here we just set a variable $var inside our function, notice we already
		//have a variable called var in the first line of out code? it will not overwrite it.
		//variables made inside the function are used only inside the function that they were.
		//made in. 
 
		return $var;
		//return $var is the last part to this function and will output whatever $var may be to the page
		//once the function has been used within it.
	}
 
 
	$string = 'Here I have a different variable name and I would like the string it carries to be bold';
 
 
	makeBold( $string ); //Now this is where you may not understand it. When we created our function the variable 
			     //inside the brackets said $text and weve just put a variable called $string inside there!
			     //Do not fear this was intentional, I promise. The $text variable in the brackets when we created our
			     //function was only meant to show where the variable or string would be going once we put
			     //our function to use.
 
	echo '<br />';//dont want out text all bunched up now do we :)
 
	makeBold( 'I would like to be bold please' ); //you can also enter just a string inside the brackets of our function
						      //the string will replace the variable $text when we created our function
						      //if that helps you understand it better.
 
	echo '<br />';//dont want out text all bunched up now do we :)
 
	echo $var; //Finally we echo the variable we created before we created the function just to show that 
		   //a variable with the same name inside the function will not overwrite it.
?>

Now if you read all the comments I made within the code you should hopefully have a better grasp of what a function does and how it works.

conclusion

A simple function like this would be used to repeat a simple task or piece of code over and over without having to rewrite the code over and over again.
e.g.:

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<?php
$var = 10;
$var2 = 11;
$var3 = 12;
 
$var = $var / 5 + 1 * 2;
echo $var.'<br />';
 
$var2 = $var2 / 5 + 1 * 2;
echo $var.'<br />';
 
$var2 = $var2 / 5 + 1 * 2;
echo $var.'<br />';
?>

This piece of code requires you to redo the same calculations over and over which makes your code look messy and it is inefficient.

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<?php
function math( $var ){
$var = $var / 5 + 1 * 2;
return $var.'<br />';
}
math( '10' );
math( '11' );
math( '12' );
?>

Now on a small scale like this it may not seem like a massive difference but on a large scale it makes a massive difference and greatly reduces your code.

If you liked or found this helpful please comment or if you didn’t please comment and ask why and maybe I can help :)