Arrays & Functions - DWCS Course 2025-26

Introduction to Arrays

Arrays are essential data structures in PHP that store multiple values in a single variable. PHP supports both indexed and associative arrays.

Array Types

Indexed Arrays

Arrays with numeric indices starting from 0:

<?php
// Creating indexed arrays
$numeros = [1, 2, 3, 4, 5];
$nombres = array("Juan", "María", "Pedro");

// Accessing elements
echo $numeros[0];  // Output: 1
echo $nombres[2];  // Output: Pedro

// Adding elements
$numeros[] = 6;  // Adds to the end
?>

Associative Arrays

Arrays with named keys:

<?php
// Creating associative arrays
$persona = [
    'nombre' => 'Juan',
    'apellido' => 'García',
    'edad' => 25
];

// Alternative syntax
$curso = array(
    'nombre' => 'DWCS',
    'año' => 2025,
    'activo' => true
);

// Accessing elements
echo $persona['nombre'];  // Output: Juan
echo $curso['año'];       // Output: 2025
?>

Multidimensional Arrays

Arrays containing other arrays:

<?php
// 2D array (matrix)
$matriz = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
];

// Accessing elements
echo $matriz[0][0];  // Output: 1
echo $matriz[1][2];  // Output: 6

// Creating matrix with loops
for ($fila = 0; $fila < 3; $fila++) {
    for ($columna = 0; $columna < 3; $columna++) {
        $matriz[$fila][$columna] = rand(0, 100);
    }
}
?>

Array Operations

Counting Elements

<?php
$numeros = [1, 2, 3, 4, 5];
$cantidad = count($numeros);  // Returns 5

// For multidimensional arrays
$matriz = [[1, 2], [3, 4], [5, 6]];
$filas = count($matriz);          // Returns 3
$columnas = count($matriz[0]);    // Returns 2
?>

Adding Elements

<?php
$frutas = ['manzana', 'naranja'];

// Add to end
$frutas[] = 'plátano';
array_push($frutas, 'pera', 'uva');

print_r($frutas);
// Output: Array ( [0] => manzana [1] => naranja [2] => plátano [3] => pera [4] => uva )
?>

Removing Elements

<?php
$frutas = ['manzana', 'naranja', 'plátano', 'pera'];

// Remove from end
$ultima = array_pop($frutas);  // Returns 'pera'

// Remove from beginning
$primera = array_shift($frutas);  // Returns 'manzana'

// Remove specific element
unset($frutas[1]);  // Removes 'plátano'

// Reset array indices
$frutas = array_values($frutas);
?>

Iterating Over Arrays

Foreach Loop

The most common way to iterate over arrays:

Indexed Array
Associative Array
Multidimensional

<?php
$numeros = [1, 2, 3, 4, 5];

foreach ($numeros as $numero) {
    echo $numero . " ";
}
// Output: 1 2 3 4 5
?>

<?php
$persona = [
    'nombre' => 'Juan',
    'apellido' => 'García',
    'edad' => 25
];

foreach ($persona as $clave => $valor) {
    echo "$clave: $valor<br>";
}
// Output:
// nombre: Juan
// apellido: García
// edad: 25
?>

<?php
$matriz = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
];

foreach ($matriz as $fila) {
    foreach ($fila as $valor) {
        echo $valor . " ";
    }
    echo "<br>";
}
// Output:
// 1 2 3
// 4 5 6
// 7 8 9
?>

For Loop with Arrays

<?php
$numeros = [10, 20, 30, 40, 50];

for ($i = 0; $i < count($numeros); $i++) {
    echo "Índice $i: {$numeros[$i]}<br>";
}
?>

Array Functions

Searching Arrays

<?php
$frutas = ['manzana', 'naranja', 'plátano', 'pera'];

// Check if value exists
if (in_array('naranja', $frutas)) {
    echo "Naranja encontrada";
}

// Find position
$posicion = array_search('plátano', $frutas);  // Returns 2

// Check if key exists
if (array_key_exists('nombre', $persona)) {
    echo "Clave existe";
}

// Alternative for key checking
if (isset($persona['nombre'])) {
    echo "Clave existe";
}
?>

Sorting Arrays

<?php
$numeros = [5, 2, 8, 1, 9];

// Sort ascending
sort($numeros);
print_r($numeros);  // [1, 2, 5, 8, 9]

// Sort descending
rsort($numeros);
print_r($numeros);  // [9, 8, 5, 2, 1]
?>

Merging Arrays

<?php
$array1 = [1, 2, 3];
$array2 = [4, 5, 6];

// Merge arrays
$combinado = array_merge($array1, $array2);
print_r($combinado);  // [1, 2, 3, 4, 5, 6]

// Merge associative arrays
$datos1 = ['nombre' => 'Juan', 'edad' => 25];
$datos2 = ['ciudad' => 'Madrid', 'país' => 'España'];

$completo = array_merge($datos1, $datos2);
print_r($completo);
// Array ( [nombre] => Juan [edad] => 25 [ciudad] => Madrid [país] => España )
?>

Form Arrays

PHP can receive form data as arrays:

<form action="<?php echo $_SERVER['PHP_SELF'] ?>" method="get">
    <?php
    $filas = 3;
    $columnas = 3;
    
    for ($fila = 0; $fila < $filas; $fila++) {
        for ($columna = 0; $columna < $columnas; $columna++) {
            echo "<input type='number' name='matriz[$fila][$columna]' />";
        }
        echo "<br>";
    }
    ?>
    <button type="submit">Enviar</button>
</form>

<?php
if (isset($_GET['matriz'])) {
    $matriz = $_GET['matriz'];
    
    // Process matrix
    foreach ($matriz as $fila => $columnas) {
        foreach ($columnas as $columna => $valor) {
            echo "[$fila][$columna] = $valor ";
        }
        echo "<br>";
    }
}
?>

Functions

Functions allow you to organize and reuse code effectively.

Basic Function Syntax

<?php
// Simple function
function saludar() {
    echo "¡Hola!";
}

// Call the function
saludar();  // Output: ¡Hola!
?>

Function Parameters

Required Parameters
Default Parameters
Type Hints

<?php
function sumar($a, $b) {
    return $a + $b;
}

$resultado = sumar(5, 3);  // Returns 8
echo $resultado;
?>

<?php
function saludar($nombre = "Usuario") {
    return "¡Hola, $nombre!";
}

echo saludar();          // Output: ¡Hola, Usuario!
echo saludar("Juan");    // Output: ¡Hola, Juan!
?>

<?php
function multiplicar(int $a, int $b): int {
    return $a * $b;
}

$resultado = multiplicar(4, 5);  // Returns 20
?>

Return Values

Functions can return different types of values:

<?php
function esPrimo(int $numero): bool {
    $raiz = floor(sqrt($numero));
    $i = 2;

    while (($i <= $raiz) && (($numero % $i) !== 0)) {
        $i++;
    }

    if ($i > $raiz) {
        return $numero === 1 ? false : true;
    } else {
        return false;
    }
}

// Usage
for ($i = 1; $i <= 100; $i++) {
    if (esPrimo($i)) {
        echo "$i ";
    }
}
?>

Pass by Reference

Modify variables passed to functions using the & operator:

<?php
// Recursive function with reference parameter
function espejo($numero, &$invertido) {
    if ($numero == 0) {
        return;
    } else {
        $invertido .= ($numero % 10);
        espejo((int)($numero / 10), $invertido);
    }
}

// Usage
$numero = 12345;
$invertido = "";
espejo($numero, $invertido);
echo $invertido;  // Output: 54321
?>

Practical Function Examples

Matrix Display Function

From the course materials - a function that creates and displays a matrix:

<?php
function imprimirMatriz(int $filas, int $columnas): array {
    echo "<br><br>";
    echo "<table class='matrix'>";
    echo "<thead></thead>";
    echo "<tbody>";

    $activa = false;
    if (isset($_GET['matriz'])) {
        $matriz = $_GET['matriz'];
        $activa = true;
    } else {
        // Add random default values for easier debugging
        for ($fila = 0; $fila < $filas; $fila++) {
            for ($columna = 0; $columna < $columnas; $columna++) {
                $matriz[$fila][$columna] = rand(0, 100);
            }
        }
        $activa = true;
    }

    // Add rows to the table
    for ($fila = 0; $fila < $filas; $fila++) {
        echo "<tr>";

        for ($columna = 0; $columna < $columnas; $columna++) {
            echo "<td>";
            echo "<input type='number' name=\"matriz[$fila][$columna]\" " . 
                 ($activa ? "value=\"{$matriz[$fila][$columna]}\" " : '') . "/>";
            echo "</td>";
        }

        echo "</tr>";
    }
    
    echo "</tbody>";
    echo "</table>";

    return $matriz;
}

// Usage
$numeroFilas = 3;
$numeroColumnas = 3;
$matriz = imprimirMatriz($numeroFilas, $numeroColumnas);
?>

String Encoding Function

Advanced multibyte string processing from the course:

<?php
/**
 * Encode a message using a custom cipher
 * 
 * @param string $mensaje Message to encode
 * @param string $codigo Cipher code
 * @param string $cadenaReferencia Reference string for character mapping
 * @return string Encoded message or error message
 */
function codificarMensaje(string $mensaje, string $codigo, string $cadenaReferencia): string {
    $cifrado = $mensaje;
    $posicion = 0;

    for ($i = 0; $i < mb_strlen($mensaje); $i++) {
        // Leave spaces as-is
        if (mb_substr($mensaje, $i, 1) === " ") {
            $cifrado = mb_substr($cifrado, 0, $i) . " " . 
                       mb_substr($cifrado, $i + 1, strlen($cifrado));
        } else {
            // Find character position in reference string
            $posicion = mb_strpos($cadenaReferencia, mb_substr($mensaje, $i, 1));

            if ($posicion === false) {
                return "Carácter en mensaje no soportado: '" . 
                       mb_substr($mensaje, $i, 1) . "' : PROCESO ABORTADO";
            } else if (mb_substr($codigo, $posicion, 1) === "-") {
                // Skip character
                ;
            } else if (mb_substr($codigo, $posicion, 1) === '.') {
                // Mark for deletion (use ^ as placeholder)
                $cifrado = mb_substr($cifrado, 0, $i) . "^" . 
                           mb_substr($cifrado, $i + 1, mb_strlen($cifrado));
            } else {
                // Replace character
                $cifrado = mb_substr($cifrado, 0, $i) . 
                           mb_substr($codigo, $posicion, 1) . 
                           mb_substr($cifrado, $i + 1, strlen($cifrado));
            }
        }
    }

    // Remove deleted characters
    $cifrado = str_replace('^', '', $cifrado);
  
    return $cifrado;
}

// Usage
$cadenaReferencia = 'abcdefghijklmnñopqrstuvwxyzABCDEFGHIJKLMNÑOPQRSTUVWXYZ0123456789';
$codigo = 'fkdjfklhgosidfowheoihfosfdlkfjlkdfjoiwejf2343sd987238479lkdjflk4';
$mensaje = "Hola Mundo";

$mensajeCodificado = codificarMensaje($mensaje, $codigo, $cadenaReferencia);
echo "Mensaje codificado: $mensajeCodificado";
?>

When working with UTF-8 strings (special characters, emojis), always use multibyte string functions (mb_strlen, mb_substr, mb_strpos) instead of regular string functions.

Code Organization with Include

Organize code into separate files for better maintainability:

File Structure

proyecto/
├── index.php
├── sanitizar.php
├── formulario1.php
├── formulario2.php
└── formulario3.php

Using Include

<?php
// Include validation functions
include "sanitizar.php";

$estado = !isset($_GET['estado']) ? 0 : intval($_GET['estado']);
$numero = !isset($_GET['numero']) || 
          !formatoEnteroValido($_GET['numero']) 
          ? "INVALIDO" 
          : intval($_GET['numero']);

switch($estado) {
    case 0:
        $estado = 1;
        include "formulario1.php";
        break;

    case 1:
        $estado = 1;
        if ($numero === "INVALIDO") {
            include "formulario2.php";
        } else {
            include "formulario3.php";
        }
        break;

    default:
        throw new Exception("Estado no válido: " . $estado);
}
?>

Include vs Require

include
require

<?php
// Produces warning if file not found, script continues
include "config.php";
include_once "functions.php";  // Include only once
?>

<?php
// Produces fatal error if file not found, script stops
require "database.php";
require_once "classes.php";  // Require only once
?>

Use require for critical files (database connections, core functions). Use include for optional components (templates, plugins).

Variable Scope

Understanding variable scope is crucial for function development:

Local Scope

Variables declared inside a function are local:

<?php
function prueba() {
    $local = "Solo visible dentro de la función";
    echo $local;
}

prueba();
// echo $local;  // Error: undefined variable
?>

Global Scope

Access global variables inside functions:

<?php
$global = "Variable global";

function mostrar() {
    global $global;
    echo $global;
}

mostrar();  // Output: Variable global
?>

Static Variables

Preserve values between function calls:

<?php
function contador() {
    static $count = 0;
    $count++;
    echo $count;
}

contador();  // Output: 1
contador();  // Output: 2
contador();  // Output: 3
?>

Anonymous Functions (Closures)

PHP supports anonymous functions for callbacks:

<?php
// Anonymous function
$cuadrado = function($n) {
    return $n * $n;
};

echo $cuadrado(5);  // Output: 25

// Array map with anonymous function
$numeros = [1, 2, 3, 4, 5];
$cuadrados = array_map(function($n) {
    return $n * $n;
}, $numeros);

print_r($cuadrados);  // [1, 4, 9, 16, 25]

// Array filter
$pares = array_filter($numeros, function($n) {
    return $n % 2 === 0;
});

print_r($pares);  // [2, 4]
?>

Array Manipulation Best Practices

Use Appropriate Array Type

Choose indexed arrays for lists, associative arrays for structured data:

<?php
// Good: structured data
$usuario = [
    'id' => 1,
    'nombre' => 'Juan',
    'email' => 'juan@example.com'
];

// Good: simple list
$tags = ['php', 'mysql', 'javascript'];
?>

Validate Array Data

Always check if array keys exist before accessing:

<?php
if (isset($matriz[$fila][$columna])) {
    $valor = $matriz[$fila][$columna];
} else {
    $valor = 0;  // Default value
}
?>

Use Built-in Functions

Leverage PHP’s extensive array function library:

<?php
// Instead of manual loops
$suma = array_sum($numeros);
$promedio = array_sum($numeros) / count($numeros);
$max = max($numeros);
$min = min($numeros);
?>

Complete Example: Prime Number Function

Here’s a complete working example from the course:

<!DOCTYPE html>
<html lang="es">
<head>
    <meta charset="UTF-8">
    <title>Números Primos</title>
</head>
<body>
    <div class="primos">
        <pre>
<?php
/**
 * Check if a number is prime
 * 
 * @param int $numero Number to check
 * @return bool true if prime, false otherwise
 */
function esPrimo(int $numero): bool {
    $raiz = floor(sqrt($numero));
    $i = 2;

    // By mathematical property, only need to check up to square root
    while (($i <= $raiz) && (($numero % $i) !== 0)) {
        $i++;
    }

    if ($i > $raiz) {
        return $numero === 1 ? false : true;
    } else {
        return false;
    }
}

// Display first 100 numbers, showing primes
for ($i = 1; $i <= 100; $i++) {
    echo (esPrimo($i) ? (" " . ($i < 10 ? " " . $i : $i) . " ") : " -- ");
    echo (($i % 10) === 0 ? "<br>" : "");
}
?>
        </pre>
    </div>
</body>
</html>

Next Steps

Now that you understand arrays and functions, explore:

Object-Oriented PHP - Learn classes and objects
Database Operations - Work with database result arrays
Sessions & Cookies - Manage user data with arrays

Get Started

PHP Fundamentals

Database Programming

Session Management

Web Services

AJAX & Jaxon

API Integration

Assignments & Exams

​Introduction to Arrays

​Array Types

​Indexed Arrays

​Associative Arrays

​Multidimensional Arrays

​Array Operations

​Counting Elements

​Adding Elements

​Removing Elements

​Iterating Over Arrays

​Foreach Loop

​For Loop with Arrays

​Array Functions

​Searching Arrays

​Sorting Arrays

​Merging Arrays

​Form Arrays

​Functions

​Basic Function Syntax

​Function Parameters

​Return Values

​Pass by Reference

​Practical Function Examples

​Matrix Display Function

​String Encoding Function

​Code Organization with Include

​File Structure

​Using Include

​Include vs Require

​Variable Scope

​Anonymous Functions (Closures)

​Array Manipulation Best Practices

​Complete Example: Prime Number Function

​Next Steps

Introduction to Arrays

Array Types

Indexed Arrays

Associative Arrays

Multidimensional Arrays

Array Operations

Counting Elements

Adding Elements

Removing Elements

Iterating Over Arrays

Foreach Loop

For Loop with Arrays

Array Functions

Searching Arrays

Sorting Arrays

Merging Arrays

Form Arrays

Functions

Basic Function Syntax

Function Parameters

Return Values

Pass by Reference

Practical Function Examples

Matrix Display Function

String Encoding Function

Code Organization with Include

File Structure

Using Include

Include vs Require

Variable Scope

Anonymous Functions (Closures)

Array Manipulation Best Practices

Complete Example: Prime Number Function

Next Steps