PHP Basics

Introduction to PHP

PHP (Hypertext Preprocessor) is a server-side scripting language designed for web development. PHP code is embedded within HTML and executed on the server before being sent to the client’s browser.

Basic PHP Syntax

PHP code blocks are enclosed in <?php ?> tags. Every PHP statement should end with a semicolon.

<?php
// Single-line comment
/* Multi-line
   comment */
echo "Hello, World!";
?>

PHP files typically have a .php extension and can contain a mix of HTML and PHP code.

Variables and Data Types

Variables in PHP start with the $ symbol and don’t require explicit type declarations.

Variable Declaration

<?php
$numero1 = 10;           // Integer
$numero2 = 20;           // Integer
$precio = 99.99;         // Float
$nombre = "Juan";        // String
$activo = true;          // Boolean
?>

Type Casting

PHP automatically converts between types, but you can explicitly cast values:

<?php
$valorU = empty($_GET['u']) ? "VACIO": $_GET['u'];
$valorA = empty($_GET['a']) ? "VACIO": $_GET['a'];

// Explicit float casting
$resultado = (float) $valorU + $valorA * $valorT;
?>

Always validate and sanitize user input from forms to prevent security vulnerabilities.

Operators

Arithmetic Operators

PHP supports standard arithmetic operations:

<?php
$numero1 = $_GET['numero1'];
$numero2 = $_GET['numero2'];

echo "La suma es: " . ($numero1 + $numero2);
echo "La resta es: " . ($numero1 - $numero2);
echo "El producto es: " . ($numero1 * $numero2);
echo "El resto es: " . ($numero1 % $numero2);
?>

Comparison Operators

<?php
$a = 10;
$b = 20;

$a == $b   // Equal (value)
$a === $b  // Identical (value and type)
$a != $b   // Not equal
$a !== $b  // Not identical
$a < $b    // Less than
$a > $b    // Greater than
$a <= $b   // Less than or equal
$a >= $b   // Greater than or equal
?>

Logical Operators

<?php
$edad = 25;
$tieneLicencia = true;

// AND operator
if ($edad >= 18 && $tieneLicencia) {
    echo "Puede conducir";
}

// OR operator
if ($edad < 18 || !$tieneLicencia) {
    echo "No puede conducir";
}
?>

Control Structures

Conditional Statements

if-else
switch

<?php
$entero1 = $_GET['entero1'];
$entero2 = $_GET['entero2'];
$entero3 = $_GET['entero3'];

// Find the largest number
$mayor = $entero1;
if ($entero1 < $entero2) {
    $mayor = $entero2;
    if ($entero2 < $entero3) {
        $mayor = $entero3;
    }
} else {
    if ($entero1 < $entero3) {
        $mayor = $entero3;
    }
}

// Find the smallest number
$menor = $entero1;
if ($entero2 < $entero1) {
    $menor = $entero2;
    if ($entero3 < $entero2) {
        $menor = $entero3;
    }
} else {
    if ($entero3 < $entero1) {
        $menor = $entero3;
    }
}

echo "El mayor es: " . $mayor;
echo "El menor es: " . $menor;
?>

<?php
$estado = intval($_GET['estado']);

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

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

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

Loops

For Loop

Use for loops when you know the number of iterations:

<?php
for ($i = 0; $i <= 10; $i++) {
    $cuadrado = $i * $i;
    $cubo = $i * $i * $i;
    echo "Número: $i\tCuadrado: $cuadrado\tCubo: $cubo\n";
}
?>

While Loop

Use while loops for condition-based iteration:

<?php
$entero = $_GET['entero'];
$digitos = "";

while ($entero > 0) {
    $digitos = ($entero % 10) . "   " . $digitos;
    $entero = floor($entero / 10);
}

echo "Dígitos separados: " . $digitos;
?>

Foreach Loop

Use foreach to iterate over arrays (covered in Arrays & Functions):

<?php
$numeros = [1, 2, 3, 4, 5];
foreach ($numeros as $numero) {
    echo $numero . " ";
}
?>

String Manipulation

String Concatenation

<?php
$nombre = "Juan";
$apellido = "García";

// Using dot operator
$nombreCompleto = $nombre . " " . $apellido;

// Using double quotes (variable interpolation)
echo "Nombre: $nombre $apellido";

// Using curly braces for clarity
echo "Nombre: {$nombre} {$apellido}";
?>

Heredoc Syntax

Heredoc is useful for multi-line strings with embedded variables:

<?php
$numero1 = 10;
$numero2 = 20;

echo <<<MARCA
<p>
    <label for="numero1">Introduzca el primer número:</label>
    <input type="number" id="numero1" name="numero1" value="{$numero1}"/>
</p>
<p>
    <label for="numero2">Introduzca el segundo número:</label>
    <input type="number" id="numero2" name="numero2" value="{$numero2}" />
</p>
MARCA;
?>

Constants

Define constants using define() or the const keyword:

<?php
// Using define()
define('IMPUESTO_ESTATAL', 0.05);
define('IMPUESTO_AUTONOMICO', 0.04);

// Using const
const PI = 3.14159;

// Usage
$totalMensualVentas = 1000;
$liquido = $totalMensualVentas / (1 + IMPUESTO_AUTONOMICO + IMPUESTO_ESTATAL);
$impuestosEstatales = $liquido * IMPUESTO_ESTATAL;
?>

Constants are case-sensitive by default and conventionally written in UPPERCASE.

Type Checking and Validation

Empty and Isset

<?php
// Check if variable is set
if (isset($_GET['nombre'])) {
    echo "Variable exists";
}

// Check if variable is empty
if (empty($_GET['email'])) {
    echo "Email is required";
}

// Combining checks
$valor = empty($_GET['dato']) ? "VACIO" : $_GET['dato'];
?>

Type Validation

<?php
$numero = $_GET['numero'];

// Check if numeric
if (is_numeric($numero)) {
    echo "Es numérico";
}

// Check specific types
is_int($numero);      // Integer
is_float($numero);    // Float
is_string($numero);   // String
is_bool($numero);     // Boolean
is_array($numero);    // Array
?>

Number Formatting

Format numbers for display with number_format():

<?php
$totalMensualVentas = 1234.5678;
$liquido = 456.789;

// Format with 2 decimals, comma as decimal separator
$totalMensualVentas = number_format($totalMensualVentas, 2, ",", "");
$liquido = number_format($liquido, 2, ",", "");

echo "Total: {$totalMensualVentas} €";
echo "Líquido: {$liquido} €";
?>

Superglobal Variables

PHP provides several built-in superglobal arrays:

$_GET: Data from URL parameters or GET forms
$_POST: Data from POST forms
$_SERVER: Server and execution environment information
$_SESSION: Session variables
$_COOKIE: Cookie values

Using $_SERVER

<?php
// Current script filename
echo $_SERVER['PHP_SELF'];

// Server name
echo $_SERVER['SERVER_NAME'];

// Request method (GET, POST, etc.)
echo $_SERVER['REQUEST_METHOD'];
?>

Best Practices

Always Validate Input

Never trust user input. Always validate and sanitize data from forms:

<?php
$numero = !isset($_GET['numero']) || 
          preg_match("/^[+-]?\d+$/", $_GET['numero']) !== 1 
          ? "INVALIDO" 
          : intval($_GET['numero']);
?>

Use Meaningful Variable Names

Choose descriptive variable names that reflect their purpose:

// Good
$totalMensualVentas = 1000;
$impuestosAutonomicos = 40;

// Bad
$x = 1000;
$temp = 40;

Handle Errors Gracefully

Always provide user-friendly error messages:

<?php
if ($entero === "" || $entero < 0) {
    echo '<p style="color: red">El número debe ser positivo</p>';
}
?>

Practical Example: Form Processing

Here’s a complete example from the course materials demonstrating basic PHP concepts:

<!DOCTYPE html>
<html lang="es">
<head>
    <meta charset="UTF-8">
    <title>PHP Form Example</title>
</head>
<body style="font-family: monospace">
    <form action="<?php echo $_SERVER['PHP_SELF'] ?>" method="get">
<?php
    $botonEnviar = !isset($_GET['botonEnviar']) || 
                   $_GET['botonEnviar'] != "Enviar" ? false : true;
    $botonReset = !isset($_GET['botonReset']) || 
                  $_GET['botonReset'] != "Reset" ? false : true;

    $entero1 = empty($_GET['entero1']) ? "" : $_GET['entero1'];
    $entero2 = empty($_GET['entero2']) ? "" : $_GET['entero2'];
    $entero3 = empty($_GET['entero3']) ? "" : $_GET['entero3'];

    if ($botonReset) {
        $entero1 = "";
        $entero2 = "";
        $entero3 = "";
    }

    echo <<<MARCA
    <p>
        <label for="numero1">Introduzca primer entero:</label>
        <input type="number" id="numero1" name="entero1" value="{$entero1}" />
    </p>
    <p>
        <label for="numero2">Introduzca segundo entero:</label>
        <input type="number" id="numero2" name="entero2" value="{$entero2}" />
    </p>
    <p>
        <label for="numero3">Introduzca tercer entero:</label>
        <input type="number" id="numero3" name="entero3" value="{$entero3}" />
    </p>
MARCA;

    if ($entero1 === "" || $entero2 === "" || $entero3 === "") {
        if ($botonEnviar) {
            echo '<p style="color: red">Rellene todos los campos</p>';
        }
    } else {
        $suma = $entero1 + $entero2 + $entero3;
        $media = $suma / 3;
        $producto = $entero1 * $entero2 * $entero3;

        echo "<p>La suma es: $suma</p>";
        echo "<p>La media es: $media</p>";
        echo "<p>El producto es: $producto</p>";
    }
?>
        <button type="submit" name="botonEnviar" value="Enviar">Enviar</button>
        <button type="submit" name="botonReset" value="Reset">Reset</button>
    </form>
</body>
</html>

Next Steps

Now that you understand PHP basics, continue to:

Forms & Validation - Learn to process and validate form data
Arrays & Functions - Master arrays and create reusable functions

Get Started

PHP Fundamentals

Database Programming

Session Management

Web Services

AJAX & Jaxon

API Integration

Assignments & Exams

Introduction to PHP

Basic PHP Syntax

Variables and Data Types

Variable Declaration

Type Casting

Operators

Arithmetic Operators

Comparison Operators

Logical Operators

Control Structures

Conditional Statements

Loops

String Manipulation

String Concatenation

Heredoc Syntax

Constants

Type Checking and Validation

Empty and Isset

Type Validation

Number Formatting

Superglobal Variables

Using $_SERVER

Best Practices

Practical Example: Form Processing

Next Steps

Get Started

PHP Fundamentals

Database Programming

Session Management

Web Services

AJAX & Jaxon

API Integration

Assignments & Exams

​Introduction to PHP

​Basic PHP Syntax

​Variables and Data Types

​Variable Declaration

​Type Casting

​Operators

​Arithmetic Operators

​Comparison Operators

​Logical Operators

​Control Structures

​Conditional Statements

​Loops

​String Manipulation

​String Concatenation

​Heredoc Syntax

​Constants

​Type Checking and Validation

​Empty and Isset

​Type Validation

​Number Formatting

​Superglobal Variables

​Using $_SERVER

​Best Practices

​Practical Example: Form Processing

​Next Steps

Introduction to PHP

Basic PHP Syntax

Variables and Data Types

Variable Declaration

Type Casting

Operators

Arithmetic Operators

Comparison Operators

Logical Operators

Control Structures

Conditional Statements

Loops

String Manipulation

String Concatenation

Heredoc Syntax

Constants

Type Checking and Validation

Empty and Isset

Type Validation

Number Formatting

Superglobal Variables

Using $_SERVER

Best Practices

Practical Example: Form Processing

Next Steps