Aim

To build a menu-driven calculator in PHP that dispatches the user's choice through a switch-case construct, including break, default and a division-by-zero guard.

Theory

A switch statement compares one subject expression against a series of case labels and starts executing at the first label that matches. Advanced points every examiner probes:

• Loose comparison: switch matches cases with == semantics, so case "1" would match integer 1. PHP 8's match expression is the strict (===) alternative that also returns a value and needs no break.
• Fallthrough: without break, execution continues into the next case's body. That is occasionally useful (grouping cases) but is a classic source of bugs — every case here ends with break.
• default runs when nothing matches; placing it last is a convention, not a requirement.
• Menu-driven design is the standard pattern for console/CGI utilities: display numbered options, read a choice, dispatch with switch, and loop until exit. It cleanly separates input, dispatch and action concerns.
• Defensive programming: any arithmetic path that divides must guard the denominator ($b != 0) because integer division by zero throws a DivisionByZeroError in PHP 8.

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 p04_menu_switch.php in C:\xampp\htdocs\wbplab.
3. Run http://localhost/wbplab/p04_menu_switch.php in the browser or php p04_menu_switch.php in a terminal.
4. Change $b to 0 and observe the guarded division message; add a bogus choice such as 9 to $demoChoices to see default fire.

Explanation of the Code

• $a = 20 and $b = 5 are the fixed operands; $demoChoices = [1, 2, 3, 4] simulates a user selecting every menu option in turn so the program is runnable without interactive input (in a real form, the choice would arrive via $_POST).
• The menu itself is printed once with echo before the loop.
• Inside foreach, switch ($choice) dispatches: case 1 prints the sum ($a + $b), case 2 the difference, case 3 the product.
• case 4 demonstrates the guard: it divides only when $b != 0, otherwise prints Division by zero not allowed. — the check belongs inside the case so other operations remain unaffected.
• Each case ends in break to prevent fallthrough, and default catches any invalid menu number.

Expected Output

After the four-line menu, the program prints four blocks: Choice: 1 / Addition: 25, Choice: 2 / Subtraction: 15, Choice: 3 / Multiplication: 100, Choice: 4 / Division: 4 — each block separated by a blank line.

🎯 Viva Questions

1. What happens if break is omitted from a case? Execution falls through and runs the next case's statements too.
2. How does switch compare values? Loosely (==), with type juggling; match in PHP 8 compares strictly.
3. When does default execute? Only when no case label matches the subject expression.
4. Why guard case 4 with $b != 0? Division by zero raises DivisionByZeroError (fatal) in PHP 8.
5. switch vs match — two differences. match uses strict comparison and returns a value; it also has no fallthrough.
6. Why is a menu-driven structure preferred in lab utilities? It separates input, dispatch and action, making each operation independently testable.

CO Mapping

CO1, CO2