PHP Functions

PHP Built-in Functions

• ★ PHP has over 1000 built-in functions that can be called directly, from within a script, to perform a specific task.
• ★ Please check out our PHP reference for a complete overview of the PHP built-in functions.

PHP User Defined Functions

Besides the built-in PHP functions, it is possible to create your own functions.

• ★ A function is a block of statements that can be used repeatedly in a program.
• ★ A function will not execute automatically when a page loads.
• ★ A function will be executed by a call to the function.
• ★ Syntax:

				function functionName() {
  					code to be executed;
				}
			

• ★ Example:

				<?php
						function writeMsg() {
 							 echo "Hello world!";
						}

						writeMsg(); // call the function
				?>
			

PHP Function Arguments

• ★ The following example has a function with one argument ($fname). When the familyName() function is called, we also pass along a name (e.g. Jani), and the name is used inside the function:

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

				familyName("Jani");
				familyName("Hege");
				familyName("Stale");
				familyName("Kai Jim");
				familyName("Borge");
			?>
		

• ★ The following example has a function with three arguments ($fname, $lname, and $year):

			<?php
				function fullName($fname, $lname, $year) {
  					echo "$fname $lname born in $year <br>";
				}

				fullName("Hege", "Mark", "1975");
				fullName("Stale", "Love", "1978");
				fullName("Kai Jim", "Walisa", "1983");
			?>
			

• ★ You can also return values from the function instead of echoing:

				function fullName($fname, $lname, $year) {
				    return "$fname $lname born in $year";
				}

				echo fullName("Hege", "Michael", 1975) . "<br>";
			

PHP Default Argument Value

The following example shows how to use a default parameter. If we call the function setHeight() without arguments it takes the default value as argument:

			<?php 
			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);
			?>
		

With int (typed parameter)

			setHeight(75.5);     // ✅ Becomes 75
			setHeight("100");    // ✅ Converts to 100
			setHeight("tall");   // ❌ Error in strict mode
		

If you want to add more parameters with defaults, just make sure required ones come first:

			function setBoxSize($width, $height = 100, $depth = 50) {
			    echo "Box: $width x $height x $depth <br>";
			}
			
			setBoxSize(200);
			setBoxSize(200,150);
			setBoxSize(200,150,20);
		

PHP Functions - Returning values

To let a function return a value, use the return statement:

			<?php
					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);
			?>
		

Quadratic Formula Example:

			function solveQuadratic($a, $b, $c) {
			    $discriminant = ($b * $b) - (4 * $a * $c);
			
			    if ($discriminant < 0) {
			        return "No real solutions.";
			    } elseif ($discriminant == 0) {
			        $x = -$b / (2 * $a);
			        return "One real solution: x = $x";
			    } else {
			        $sqrtDisc = sqrt($discriminant);
			        $x1 = (-$b + $sqrtDisc) / (2 * $a);
			        $x2 = (-$b - $sqrtDisc) / (2 * $a);
			        return "Two real solutions: x₁ = $x1 and x₂ = $x2";
			    }
			}
			
			// Example usage:
			echo "Equation: x² + 5x + 6 = 0<br>";
			echo solveQuadratic(1, 5, 6) . "<br><br>";
			
			echo "Equation: x² + 4x + 4 = 0<br>";
			echo solveQuadratic(1, 4, 4) . "<br><br>";
			
			echo "Equation: x² + 2x + 5 = 0<br>";
			echo solveQuadratic(1, 2, 5);
		

Passing Arguments by Reference

• In PHP, arguments are usually passed by value, which means that a copy of the value is used in the function and the variable that was passed into the function cannot be changed.
• When a function argument is passed by reference, changes to the argument also change the variable that was passed in. To turn a function argument into a reference, the & operator is used:

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

					$num = 2;
					add_five($num);
					echo $num;
			?>
		

PHP Arrays

Create an Array in PHP

• ★ In PHP, older syntax array() function is used to create an array:

			<?php
				$cars = array("Volvo", "BMW", "Toyota");
				echo "I like " . $cars[0] . ", " . $cars[1] . " and " . $cars[2] . ".";
			?>
			

• ★ Short array syntax [...], introduced in PHP 5.4

					$cars = ["Volvo", "BMW", "Toyota"];
				

• ★In PHP, there are three types of arrays:
• ★ Indexed arrays - Arrays with a numeric index
• ★ Associative arrays - Arrays with named keys
• ★ Multidimensional arrays - Arrays containing one or more arrays

The count() Function

• ★ The count() function is used to return the length (the number of elements) of an array:

			<?php
				$cars = ["Volvo", "BMW", "Toyota"];
				echo count($cars);
			?>	
			

Loop Through an Indexed Array

• ★ To loop through and print all the values of an indexed array, you could use a for loop, like this:

			<?php
				$cars = ["Volvo", "BMW", "Toyota"];
				$arrlength = count($cars);

				for($x = 0; $x < $arrlength; $x++) {
 					   echo $cars[$x];
					   echo "<br>";
				}
			?>
			

PHP Associative Arrays

An associative array in PHP lets you use named keys (strings) instead of just numbers to access values.

• ★ Associative arrays are arrays that use named keys that you assign to them.

				<?php
				$age = [
				"Peter"=>"35", 
				"Ben"=>"37", 
				"Joe"=>"43"];
				
				echo "Peter is " . $age['Peter'] . " years old.";
				?>
			

Loop Through an Associative Array

• ★ To loop through and print all the values of an associative array, you could use a foreach loop, like this:

				<?php
					$age = [
					"Peter"=>"35", 
					"Ben"=>"37", 
					"Joe"=>"43"];

					foreach($age as $key => $value) {
 							echo "Key=" . $key . ", Value=" . $value;
				                        echo "<br>";
					}
				?>
			

PHP Contact List Webpage using Associative Arrays

	
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Contact List</title>
    <style>
	body {
	    font-family: Arial, sans-serif;
	    padding: 20px;
	    background: #f8f8f8;
	}
	h1 {
	    color: #333;
	}
	table {
	    border-collapse: collapse;
	    width: 80%;
	    background-color: #fff;
	}
	th, td {
	    border: 1px solid #ccc;
	    padding: 10px;
	    text-align: left;
	}
	th {
	    background-color: #eee;
	}
    </style>
</head>
<body>

<h1>📇 Contact List</h1>

<?php
// Our associative array of contacts
$contacts = [
    "alice" => [
	"name" => "Alice Smith",
	"email" => "alice@example.com",
	"city" => "Nashville"
    ],
    "bob" => [
	"name" => "Bob Johnson",
	"email" => "bob@example.com",
	"city" => "Memphis"
    ],
    "carol" => [
	"name" => "Carol White",
	"email" => "carol@example.com",
	"city" => "Knoxville"
    ]
];
?>

<table>
    <tr>
	<th>Name</th>
	<th>Email</th>
	<th>City</th>
    </tr>

    <?php foreach ($contacts as $id => $person) { ?>
	<tr>
	    <td><?php echo $person["name"]; ?></td>
	    <td><?php echo $person["email"]; ?></td>
	    <td><?php echo $person["city"]; ?></td>
	</tr>
    <?php } ?>
</table>

</body>
</html>
	

Reference

• ★ www.w3schools.com