Do-while loop execution model in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple do-while loop

What is the output of this PHP code?

PHP

<?php
$i = 1;
do {
    echo $i . ' ';
    $i++;
} while ($i <= 3);
?>

A No output

B 1 2

C 1 2 3

D 2 3

💡 Hint

Remember, do-while runs the loop body at least once before checking the condition.

The loop starts with i=1, prints it, increments i, then checks if i <= 3. It repeats until i becomes 4, so it prints 1 2 3.

❓ Predict Output

intermediate

Do-while loop with initial false condition

What will this PHP code output?

PHP

<?php
$j = 5;
do {
    echo $j . ' ';
    $j++;
} while ($j < 5);
?>

A 5

B No output

C 5 6

D Syntax error

💡 Hint

Do-while executes the block once before checking the condition.

Even though the condition is false initially, the loop body runs once printing 5, then condition fails and loop stops.

🔧 Debug

advanced

Identify the error in this do-while loop

What error does this PHP code produce?

PHP

<?php
$k = 0;
do {
    echo $k . ' ';
    $k++
} while ($k < 3);
?>

A SyntaxError: missing semicolon

B RuntimeError: infinite loop

C No error, outputs '0 1 2 '

D TypeError: invalid condition

💡 Hint

Check punctuation carefully inside the loop body.

The line '$k++' is missing a semicolon at the end, causing a syntax error.

❓ Predict Output

advanced

Counting iterations in a do-while loop

How many times will the loop body execute in this PHP code?

PHP

<?php
$count = 0;
$num = 10;
do {
    $count++;
    $num += 5;
} while ($num < 25);
echo $count;

A 5

B 2

C 4

D 3

💡 Hint

Trace the value of $num each iteration and count how many times the loop runs.

Initial $num=10, after 1st iteration 15, 2nd iteration 20, 3rd iteration 25. Loop stops after 3 iterations because condition fails when $num=25.

🧠 Conceptual

expert

Understanding do-while loop execution order

Which statement best describes the execution model of a do-while loop in PHP?

A The condition is checked before the loop body runs, so the body may not run at all.

B The loop body runs once before the condition is checked, guaranteeing at least one execution.

C The loop body and condition are evaluated simultaneously, so execution depends on both.

D The loop body runs only if the condition is true at the start and after each iteration.

💡 Hint

Think about what makes do-while different from while loops.

In a do-while loop, the body executes first, then the condition is checked. This ensures the loop runs at least once.