While loop execution model in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a while loop that runs as long as $count is less than 5.

PHP

<?php
$count = 0;
while ([1]) {
    echo $count . "\n";
    $count++;
}
?>

Drag options to blanks, or click blank then click option'

A$count >= 5

B$count < 5

C$count == 5

D$count > 5

Attempts:

3 left

💡 Hint

Common Mistakes

Using > instead of < in the condition

Using == which runs only if $count equals 5

The while loop continues as long as the condition is true. Here, it should run while $count is less than 5.

2fill in blank

medium

Complete the code to increment $i by 2 inside the while loop.

PHP

<?php
$i = 0;
while ($i < 10) {
    echo $i . "\n";
    [1];
}
?>

Drag options to blanks, or click blank then click option'

A$i += 2

B$i--

C$i = $i + 1

D$i = 2

Attempts:

3 left

💡 Hint

Common Mistakes

Using $i = 2 which resets the value

Using $i-- which decreases the value

To increase $i by 2 each time, use $i += 2;.

3fill in blank

hard

Fix the error in the while loop condition to avoid an infinite loop.

PHP

<?php
$num = 5;
while ([1]) {
    echo $num . "\n";
    $num--;
}
?>

Drag options to blanks, or click blank then click option'

A$num == 5

B$num = 0

C$num > 5

D$num >= 0

Attempts:

3 left

💡 Hint

Common Mistakes

Using assignment (=) instead of comparison (>=)

Using a condition that never becomes false

The condition should check if $num is greater than or equal to 0 to stop the loop properly.

4fill in blank

hard

Fill both blanks to create a while loop that prints numbers from 1 to 5.

PHP

<?php
$num = 1;
while ([1]) {
    echo $num . "\n";
    [2];
}
?>

Drag options to blanks, or click blank then click option'

A$num <= 5

B$num < 5

C$num++

D$num += 2

Attempts:

3 left

💡 Hint

Common Mistakes

Using $num < 5 which stops at 4

Incrementing $num by 2 which skips numbers

The loop should run while $num is less than or equal to 5, and $num should increase by 1 each time.

5fill in blank

hard

Fill all three blanks to create a while loop that prints even numbers from 2 to 10.

PHP

<?php
$num = [1];
while ([2]) {
    echo $num . "\n";
    [3];
}
?>

Drag options to blanks, or click blank then click option'

A2

B$num <= 10

C$num += 2

D$num < 10

Attempts:

3 left

💡 Hint

Common Mistakes

Starting $num at 1 instead of 2

Using $num < 10 which excludes 10

Incrementing by 1 instead of 2

Start $num at 2, run the loop while $num is less than or equal to 10, and increase $num by 2 each time to print even numbers.

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