Aim

To demonstrate PHP's while loop — the entry-controlled loop used when the number of iterations is not known in advance — by printing the numbers 1 to 5.

Theory

while (condition) { body } evaluates its condition before each pass. If the condition is false at the first check, the body executes zero times — that zero-iteration behaviour is the defining property of an entry-controlled loop.

Structural contrast with for: a while loop spreads the counter logic across three places — initialisation before the loop ($j = 1), the test in the header ($j <= 5), and the update inside the body ($j++). Because the update is a normal statement, forgetting it is the most common cause of infinite loops: the condition never changes, and the script runs until max_execution_time (default 30 s under Apache) kills it.

Where while genuinely shines:

• Consuming data of unknown length: while ($row = $result->fetch_assoc()) { ... } when reading MySQL rows, or while (!feof($handle)) when streaming a file.
• Polling/retry loops that end on an external state change.
• Sentinel-controlled input processing (loop until a stop value appears).

Any for loop can be rewritten as while and vice versa — the choice is about communicating intent: for says "counted repetition", while says "repeat while a state holds".

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 p05b_while.php in C:\xampp\htdocs\wbplab.
3. Run http://localhost/wbplab/p05b_while.php or php p05b_while.php.
4. Comment out $j++; and re-run to witness (and then stop) a runaway loop — this makes the role of the update statement unforgettable.
5. Change the initial value to $j = 6 and confirm the body never executes.

Explanation of the Code

• $j = 1; initialises the loop-control variable before the loop — while has no built-in initialisation slot.
• while ($j <= 5) is the guard: it is checked before every pass, so the loop admits exactly five passes.
• Inside the body, echo $j . " "; prints the current value followed by a space.
• $j++; is the progress statement — the line that guarantees the condition eventually turns false. Every correct while loop must contain something that moves the state toward termination.
• When $j reaches 6, the guard fails and execution continues after the loop.

Expected Output

WHILE LOOP:
1 2 3 4 5

Five numbers on one line; starting with $j = 6 would print only the heading.

🎯 Viva Questions

1. Minimum number of body executions of a while loop? Zero — the condition is tested before entry.
2. What causes an infinite while loop? The body never changes the variables used in the condition (e.g. missing $j++).
3. Where does initialisation live for a while loop? In ordinary statements before the loop — the construct has no initialisation section.
4. Give a real use case where while beats for. Fetching database rows: while ($row = $result->fetch_assoc()) — the count is unknown.
5. What limits a runaway PHP script under Apache? The max_execution_time ini setting (30 s by default).
6. Is while (true) ever legitimate? Yes — event/polling loops that terminate via break on an internal condition.

CO Mapping

CO1, CO2