PHP Programming Basics

Study Notes

Variables in PHP

Variables in PHP are declared with the dollar sign $ prefix followed by a unique identifier. They can hold values of varying types, such as integers, floats, booleans, strings, objects, and arrays. Assigning a value to a variable involves assigning the value to the left of the equals sign (=) to the variable name.

$myName = "John";
$myAge = 25;

You can access the stored value later with the variable name, for instance, echo $myName.

Arrays in PHP

Arrays in PHP store collections of elements, usually separated by commas. Elements can have associated keys, allowing indexed or associative array structures. Indexed arrays use numbers starting at zero, while associative arrays use arbitrary string keys. You can initialize an array with curly braces and separate elements with commas as shown below:

$people = ["Tom", "Alice", "Dave"];
$friends = array("Steven" => 22, "Laura" => 25);

Arrays are commonly used with loop constructs like foreach, enabling iteration over array entries.

Loops in PHP

Loops are crucial for repetitive tasks. The simplest form is the for loop, which iterates a given number of times:

for ($i = 0; $i < 10; ++$i) {
    echo "$i ";
}
// Output: 0 1 2 3 4 5 6 7 8 9

While loops repeat until a condition becomes false, and do..while loops repeat once regardless of truthiness:

$number = 0;
do {
    echo $number;
    $number++;
} while ($number != 10);

$number = 0;
while ($number != 10) {
    echo $number;
    $number++;
}

These commands continuously output 0, incrementing each time through till reaching 9.

Functions in PHP

Functions group routines together. They take input parameters and return a result. Here is a sample function that calculates the sum of two numbers:

function addTwoNumbers($n1, $n2) {
   return $n1+$n2;
}
echo addTwoNumbers(25, 10);  // outputs 35

To call a function, invoke the defined function name. PHP passes parameters to functions and returns values using parentheses.

Classes in PHP

Classes organize program logic into manageable units. The class keyword introduces a definition block defining properties, methods, and constants. Objects are instances of classes, inheriting characteristics and behaviors. Here is a simple class representing a person:

class Person {
    public $firstName;
    public $lastName;
    
    function __construct($fn, $ln) {
        $this->firstName = $fn;
        $this->lastName = $ln;
    }
    
    function setFullname($fullname) {
        list($f,$l) = explode (" ", $fullname);
        $this->firstName = $f;
        $this->lastName = $l;
    }
}
$me = new Person("John","Smith");
echo $me->firstName." ". $me->lastName; // John Smith

Objects can receive messages (method calls) and send messages to other objects.

Description

Learn about PHP essentials such as variables, arrays, loops, functions, and classes. This quiz covers topics like variable declaration, array initialization, loop constructs like for and while, function creation, and class definition for PHP programming.