Aim

To demonstrate PHP's do-while loop — the exit-controlled loop whose body is guaranteed to run at least once — by printing the numbers 1 to 5.

Theory

do { body } while (condition); inverts the usual order: the body executes first, and the condition is evaluated after each pass. Consequences:

• At-least-once guarantee: even if the condition is false from the start ($k = 99), the body still executes exactly one time. This is the single behavioural difference from while, which would execute zero times.
• Because the test happens on the way out, do-while is called an exit-controlled (post-tested) loop; while and for are entry-controlled (pre-tested).
• Syntax trap: the closing while (condition) must be followed by a semicolon — omitting it is a parse error. There is no such semicolon after a normal while block.
• Canonical use cases are "do, then decide whether to repeat" workflows: re-displaying a menu until the user picks Exit, prompting again until input validates, retrying a network call until it succeeds or attempts run out, and generating a random value until it is unique.
• Scope note: variables created in the body are function-scoped, not block-scoped — PHP has no block scope, so $k remains visible after the loop with value 6.

Requirements

• XAMPP/WAMP with PHP 8.x, or PHP CLI
• Code editor and a browser/terminal

Procedure

1. Start Apache from the XAMPP Control Panel.
2. Save the snippet as p05c_do_while.php in C:\xampp\htdocs\wbplab.
3. Run http://localhost/wbplab/p05c_do_while.php or php p05c_do_while.php.
4. Key experiment: set $k = 99 and re-run. The loop still prints 99 once — repeat the same experiment with a plain while and note that it prints nothing. This pair of runs is the whole point of the practical.

Explanation of the Code

• $k = 1; initialises the control variable before the loop.
• The do block runs immediately — no condition is consulted on entry. It prints $k followed by a space, then increments with $k++.
• Only then does while ($k <= 5); decide whether to jump back to the top of the block. Passes continue while the test holds.
• After printing 5, $k becomes 6, the post-test fails, and control drops out; note the terminating semicolon on the while line.

Expected Output

DO WHILE LOOP:
1 2 3 4 5

With $k = 99 the output line becomes just 99 — one guaranteed pass despite a false condition.

🎯 Viva Questions

1. Guaranteed minimum executions of a do-while body? One — the condition is only checked after the first pass.
2. Entry-controlled vs exit-controlled? Entry-controlled loops test before the body (while, for); exit-controlled test after (do-while).
3. What punctuation ends a do-while? A semicolon after while (condition) — omitting it is a syntax error.
4. Give two real use cases for do-while. Redisplaying a menu until Exit is chosen; re-prompting until user input validates.
5. Is $k accessible after the loop, and what is its value here? Yes — PHP has no block scope; it ends as 6.
6. Convert this loop to while — what changes in behaviour? With $k = 1 nothing; with any initial value above 5, while prints nothing while do-while prints once.

CO Mapping

CO1, CO2