While loop execution model in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP while loop?

Consider the following PHP code snippet. What will it print?

PHP

<?php
$i = 3;
while ($i > 0) {
    echo $i . " ";
    $i--;
}
?>

A 3 2 1

B 1 2 3

C 3 2 1 0

D 0 1 2 3

💡 Hint

Remember the loop runs while the condition is true and $i decreases each time.

The loop starts with $i = 3 and prints it. Then $i decreases by 1 each iteration until $i is 0, which stops the loop. So it prints '3 2 1 '.

❓ Predict Output

intermediate

How many times does this while loop run?

Look at this PHP code. How many times will the loop body execute?

PHP

<?php
$count = 0;
$num = 5;
while ($num > 2) {
    $count++;
    $num--;
}
echo $count;

A 5

B 4

C 3

D 2

💡 Hint

Count how many times $num is greater than 2 before the loop stops.

The loop runs while $num is 5,4,3 (3 times). When $num becomes 2, the condition fails and loop stops. So $count is 3.

🔧 Debug

advanced

Identify the error in this while loop code

This PHP code is supposed to print numbers 1 to 5 but causes an error or unexpected behavior. What is the problem?

PHP

<?php
$i = 1;
while ($i <= 5)
    echo $i . " ";
    $i++;
?>

A Variable $i is not initialized before the loop

B The condition uses <= instead of <, causing an off-by-one error

C Missing semicolon after echo statement

D The increment $i++ is outside the loop block, causing an infinite loop

💡 Hint

Check which statements are inside the loop and which are not.

Without braces, only the first statement after while is inside the loop. The $i++ runs once after loop ends, so $i never changes inside loop, causing infinite loop.

🧠 Conceptual

advanced

What happens if the while loop condition is false initially?

Consider this PHP code snippet. What will be the output?

PHP

<?php
$x = 0;
while ($x > 0) {
    echo "Looping ";
    $x--;
}
echo "Done";

A Prints only 'Done'

B Prints 'Looping ' multiple times then 'Done'

C Prints nothing

D Causes an infinite loop

💡 Hint

Think about whether the loop body runs if the condition is false at start.

Since $x is 0 and condition $x > 0 is false initially, the loop body never runs. Only 'Done' is printed.

❓ Predict Output

expert

What is the final value of $result after this while loop?

Analyze the PHP code below and find the value of $result after the loop finishes.

PHP

<?php
$n = 4;
$result = 1;
while ($n > 0) {
    $result *= $n;
    $n--;
}
echo $result;

A 10

B 24

C 0

D 1

💡 Hint

This loop multiplies $result by $n each time, decreasing $n from 4 to 1.

The loop calculates 4 * 3 * 2 * 1 = 24, so $result is 24 after the loop.

Practice

1.

What does a while loop do in PHP?

easy

A. Runs code a fixed number of times

B. Repeats code as long as a condition is true

C. Executes code only once

D. Stops the program immediately

Solution

1. Step 1: Understand the while loop purpose

   A while loop repeats its code block while the condition remains true.

2. Step 2: Compare options with definition

   Only Repeats code as long as a condition is true matches this behavior exactly.

3. Final Answer:

   Repeats code as long as a condition is true -> Option B

4. Quick Check:

   while loop = repeat while true [OK]

Hint: Remember: while loops run only if condition is true [OK]

Common Mistakes:

• Thinking while loops run a fixed number of times
• Confusing while with if statement
• Assuming while loops always run at least once

2.

Which of the following is the correct syntax for a while loop in PHP?

?

easy

A. while ($i < 5); { echo $i; $i++; }

B. while $i < 5 { echo $i; $i++; }

C. while ($i < 5) { echo $i; $i++; }

D. while ($i < 5) echo $i; $i++;

Solution

1. Step 1: Check correct while loop syntax

   In PHP, the condition must be in parentheses and the block in braces.

2. Step 2: Identify syntax errors in options

   while ($i < 5) { echo $i; $i++; } uses correct parentheses and braces. Others miss braces, have semicolon errors, or missing parentheses.

3. Final Answer:

   while ($i < 5) { echo $i; $i++; } -> Option C

4. Quick Check:

   while (condition) { code } [OK]

Hint: Use parentheses for condition and braces for code block [OK]

Common Mistakes:

• Omitting parentheses around condition
• Adding semicolon after while condition
• Not using braces for multiple statements

3.

What will be the output of this PHP code?

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

medium

A. 1 2 3

B. 1 2 3 4

C. 123

D. 2 3 4

Solution

1. Step 1: Trace the loop iterations

   Variable $i starts at 1 and increments by 1 each loop until $i > 3.

2. Step 2: Determine output each iteration

   Outputs '1 ', then '2 ', then '3 '. Loop stops after $i becomes 4.

3. Final Answer:

   1 2 3 -> Option A

4. Quick Check:

   Prints 1 to 3 with spaces [OK]

Hint: Count from start to condition limit inclusive [OK]

Common Mistakes:

• Including extra number after loop ends
• Missing spaces in output
• Confusing <= with < in condition

4.

Find the error in this PHP while loop code:

$i = 0;
while ($i < 3)
    echo $i;
    $i++;

medium

A. Condition syntax is wrong

B. echo statement is invalid

C. Variable $i is not initialized

D. Missing braces causes $i++ to run outside loop

Solution

1. Step 1: Analyze loop structure without braces

   Without braces, only the first statement after while runs in loop.

2. Step 2: Identify effect on $i++

   $i++ runs after loop ends, causing infinite loop because $i never increments inside loop.

3. Final Answer:

   Missing braces causes $i++ to run outside loop -> Option D

4. Quick Check:

   Braces needed to include all statements in loop [OK]

Hint: Use braces to group multiple statements in while loop [OK]

Common Mistakes:

• Assuming indentation controls loop body
• Forgetting to increment loop variable inside loop
• Thinking condition syntax is incorrect

5.

You want to print all even numbers from 2 to 10 using a while loop in PHP. Which code correctly does this?

?

hard

A. $i = 2;
while ($i <= 10) {
echo $i . ' ';
$i += 2;
}

B. $i = 1;
while ($i <= 10) {
if ($i % 2 == 1) echo $i . ' ';
$i++;
}

C. $i = 2;
while ($i < 10) {
echo $i . ' ';
$i += 2;
}

D. $i = 0;
while ($i <= 10) {
echo $i . ' ';
$i += 2;
}

Solution

1. Step 1: Identify correct start and condition

   Start at 2 and include 10, so condition is $i <= 10.

2. Step 2: Check increment and output

   Increment by 2 to get even numbers only, and echo with space.

3. Step 3: Compare options

   $i = 2; while ($i <= 10) { echo $i . ' '; $i += 2; } matches all criteria exactly. $i = 1; while ($i <= 10) { if ($i % 2 == 1) echo $i . ' '; $i++; } prints odd numbers: 1 3 5 7 9. $i = 2; while ($i < 10) { echo $i . ' '; $i += 2; } misses 10. $i = 0; while ($i <= 10) { echo $i . ' '; $i += 2; } starts at 0, which is not requested.

4. Final Answer:

   $i = 2; while ($i <= 10) { echo $i . ' '; $i += 2; } -> Option A

5. Quick Check:

   Start=2, end=10, step=2 [OK]

Hint: Start at 2, increment by 2, stop at 10 inclusive [OK]

Common Mistakes:

• Starting at 0 or 1 instead of 2
• Using < instead of <= to exclude 10
• Not incrementing by 2 to get even numbers