Aim

To show the application of user-defined functions in PHP — including typed parameters, return values and recursion — through three practical examples.

Theory

A user-defined function is a named, reusable block declared with the function keyword. Functions are the primary unit of abstraction: they let you name an operation once and invoke it many times, which eliminates duplication (DRY) and makes each piece independently testable.

Points the snippet exercises:

• Type declarations: function greetUser(string $name): string constrains both the parameter and the return value. In default (coercive) mode PHP converts compatible scalars; under declare(strict_types=1) a mismatch throws TypeError.
• Return values: return immediately ends the function and hands a value to the caller. A function with no return yields null. echo inside a function prints; return delivers — the caller decides what to do with a returned value, which is why returning is the cleaner design.
• Recursion: a function that calls itself, as factorial() does. Every recursive function needs a base case (if ($n <= 1) return 1;) that stops the descent, and a recursive step that moves toward it ($n * factorial($n - 1)). Each pending call occupies a stack frame, so unbounded recursion exhausts memory.
• Scope: variables inside a function are local. Outer variables are invisible unless passed as arguments (preferred), imported with global, or captured by a closure's use clause.
• Parameters may take default values (function f($x = 10)), be passed by reference (&$x), or be variadic (...$nums).

Requirements

• XAMPP/WAMP with PHP 8.x, or PHP CLI
• Code editor (VS Code); browser or terminal

Procedure

1. Start Apache from the XAMPP Control Panel.
2. Save the snippet as p08_functions.php in C:\xampp\htdocs\wbplab.
3. Run http://localhost/wbplab/p08_functions.php or php p08_functions.php.
4. Call calculateArea("5.5", "3") with string arguments and observe coercive mode converting them; then add declare(strict_types=1); at the top and re-run to see the TypeError.
5. Trace factorial(5) on paper — write out the five stacked calls down to the base case and the multiplications on the way back up.

Explanation of the Code

• greetUser(string $name): string concatenates a greeting with the . operator and returns it; the caller echoes the result — the function itself prints nothing.
• calculateArea(float $length, float $width): float returns the product $length * $width; with arguments 5.5 and 3.0 that is 16.5.
• factorial(int $n): int is recursive. The guard if ($n <= 1) return 1; is the base case (it also protects against 0 and negative inputs). Otherwise it returns $n factorial($n - 1), so factorial(5) expands to 5 4 3 2 * 1.
• The three echo statements at the bottom invoke each function and append \n for line breaks.

Expected Output

Hello, Riya
Rectangle area: 16.5
Factorial of 5: 120

Three lines: the greeting, the area 16.5, and 120 computed by five nested recursive calls.

🎯 Viva Questions

1. Difference between echo inside a function and return? echo prints immediately as a side effect; return hands the value back so the caller can print, store or reuse it.
2. What does a PHP function return if it has no return statement? null.
3. What two parts must every recursive function have? A base case that terminates recursion and a recursive step that converges toward it.
4. What happens without the $n <= 1 base case? Infinite recursion — each call adds a stack frame until PHP aborts with a fatal error.
5. How does strict_types change the typed signatures here? Scalar arguments are no longer coerced; passing "5.5" to a float parameter throws TypeError instead of converting.
6. Are PHP function names case-sensitive? No — greetUser() and GREETUSER() call the same function (variables, in contrast, are case-sensitive).

CO Mapping

CO1, CO2