Chapter 02 · Getting Started

PHP Refresher: The Basics

Before we build with objects, we need solid bricks. This chapter is a fast, friendly tour of plain PHP: variables, data types, arrays, conditions, loops and functions. If you already know these, skim it — but don't skip the functions section, because OOP is built on top of it.

Variables — labelled boxes

<?php
$name = "Chanda";        // a box called $name holding text
$age  = 21;              // a box holding a whole number
$fee  = 4500.50;         // a box holding a decimal number
$isRegistered = true;    // a box holding yes/no (true/false)

echo "Student: " . $name . ", Age: " . $age;

The dot . glues pieces of text together — it's called concatenation. There's also a shortcut: if you use double quotes, PHP looks inside the text and swaps variables for their values automatically:

echo "Student: $name, Age: $age";   // same result, less typing

Data types you'll meet daily

Arrays — a box with compartments

$courses = ["Maths", "Physics", "Programming"];

echo $courses[0];   // Maths   (first compartment)
echo $courses[2];   // Programming

Even more useful is the associative array, where each compartment has a name instead of a number — like an envelope with labelled pockets:

$student = [
    "name"    => "Mutinta",
    "age"     => 19,
    "program" => "BSc Computing"
];

echo $student["name"];      // Mutinta
echo $student["program"];   // BSc Computing

Keep this picture in mind — an associative array looks suspiciously like a "thing with properties"... which is exactly what an object is. We're laying the groundwork already!

Making decisions — if / else

$marks = 72;

if ($marks >= 75) {
    echo "Distinction!";
} elseif ($marks >= 50) {
    echo "Pass. Well done.";
} else {
    echo "Fail. Let's revise and try again.";
}

Common comparison signs: == equal, != not equal, > greater, < less, >=, <=. Use && for "and", || for "or".

Loops — doing things many times

// Print 1 to 5
for ($i = 1; $i <= 5; $i++) {
    echo "Number $i <br>";
}

// Walk through every item in an array — you will use this CONSTANTLY
$courses = ["Maths", "Physics", "Programming"];
foreach ($courses as $course) {
    echo "I am studying $course <br>";
}

With associative arrays, foreach can give you both the label and the value:

$student = ["name" => "Mutinta", "age" => 19];

foreach ($student as $key => $value) {
    echo "$key: $value <br>";
}

Functions — recipes you write once

function makeGreeting($name) {
    return "Good morning, $name! Welcome to class.";
}

echo makeGreeting("Bwalya");
echo makeGreeting("Thandiwe");

Two important words:

• Parameter — the ingredient slot in the recipe ($name).
• Return — the function hands a value back to whoever called it. echo shows something on screen; return passes it back so the caller can decide what to do with it. Returning is usually more flexible.

Parameters can have default values, and you can (and should) declare types:

function calculateFee(float $tuition, float $discount = 0): float {
    return $tuition - $discount;
}

echo calculateFee(5000);        // 5000 (no discount given)
echo calculateFee(5000, 750);   // 4250

The float before each parameter and after the ): tells PHP: "these must be numbers, and the answer will be a number." Typed code catches mistakes early — we will use types throughout this course.

<?php
function gradeOf(int $marks): string {
    if ($marks >= 75) return "A";
    if ($marks >= 65) return "B";
    if ($marks >= 50) return "C";
    return "F";
}

$results = [82, 67, 45, 91];
foreach ($results as $marks) {
    echo "$marks => " . gradeOf($marks) . "<br>";
}