Lesson 4 — Fundamentals

Variables and Data Types

PHP is loosely typed — a variable's type is determined automatically based on the value it holds, and can change as the script runs.

Core Data Types

Unlike statically typed languages, you don't declare a type when creating a PHP variable — it's inferred from the assigned value, and can be checked at runtime with functions like gettype().

PHP — Data types 
$name = "Sizwe";      // string
$age = 28;             // integer
$price = 19.99;        // float
$isEnrolled = true;    // boolean
$student = null;       // null

echo gettype($age);    // outputs: integer

Type Juggling

PHP automatically converts between types in many operations, a behaviour called type juggling. This is convenient, but can produce surprising results if you aren't paying attention to it.

PHP — Type juggling 
$result = "5" + 3;      // 8 — the string "5" is converted to an integer
$result2 = "5" . 3;     // "53" — the . operator forces string concatenation

Common Mistakes

  • Confusing the string concatenation operator (.) with the addition operator (+), which produces very different results.
  • Relying on loose comparison (==) when strict comparison (===) is what's actually needed, especially when comparing against 0 or an empty string.
  • Assuming a variable's type will never change — PHP happily lets a variable hold a string at one point and an integer later.
  • Forgetting that null is a distinct type from an empty string or 0, even though all three can behave as "falsy" in conditions.

Professional Tip

Use === (strict comparison) instead of == whenever you need to compare both value and type. This avoids common bugs where PHP's automatic type juggling makes two very different values seem equal.

Your Turn

Write a script that declares one variable of each core type, prints each one's type using gettype(), and demonstrates the difference between == and === on one comparison.

Mini Quiz

What does the . operator do when used between a string and a number in PHP?