Simple Function

Syntax
function functionName() { 
code to be executed; 
}
Example
<?php
function writeMsg() { 
echo "Hi Hello NUV!"; 
}
writeMsg(); // call the function
?>
Function with arguments 

<?php
function familyName($fname) { 
echo "$fname Refsnes.<br>"; 
} 

familyName("Koosh"); 
familyName("Dino"); 
familyName("Ronaldo"); 
familyName("Ritz"); 
familyName("Maria");
?>
                              

Using strict type Function

                              
<?php declare(strict_types=1); // strict requirement

function addNumbers(int $a, int $b) { 
return $a + $b; 
} 
echo addNumbers(5, "5 days"); 
// since strict is enabled and "5 days" is not an integer, an error will be thrown 
?>
                              

Working with Default Value

                              
<?php 
declare(strict_types=1); // strict requirement
function setHeight(int $minheight = 50) { 
echo "The height is : $minheight <br>"; 
}
setHeight(350);
setHeight(); // will use the default value of 50 
setHeight(135); 
setHeight(80);
?>
                              

Functions with return value

                              
<?php
declare(strict_types=1); // strict requirement
function sum(int $x, int $y) { 
$z = $x + $y; 
return $z; 
}
echo "5 + 10 = " . sum(5, 10) . "<br>"; 
echo "7 + 13 = " . sum(7, 13) . "<br>"; 
echo "2 + 4 = " . sum(2, 4);
?>
                              

Passing arguments by Reference

                              
<?php
function add_five(&$value) { 
$value += 5; 
}
$num = 2; 
add_five($num); 
echo $num;
?>
                              

Parameterized Function

                              
<?php
//Adding two numbers 
function add($x, $y) 
{ 
$sum = $x + $y;
echo "Sum of two numbers is = $sum <br><br>"; 
}
add(467, 943);
//Subtracting two numbers 
function sub($x, $y)
{ 
$diff = $x -$y; 
echo "Difference between two numbers is = $diff"; 
} 
sub(943, 467);
?>