Do-while loop execution model in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a do-while loop in PHP.

PHP

<?php
do [1] {
    echo "Hello";
} while (false);

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

Awhile

Bdo

Cfor

Dforeach

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'while' instead of 'do' to start the loop.

Using 'for' or 'foreach' which are different loop types.

The do keyword starts a do-while loop in PHP.

2fill in blank

medium

Complete the code to correctly write the condition part of a do-while loop.

PHP

<?php
do {
    echo "Count: $i\n";
    $i++;
} while ([1] < 5);

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

A$i

B$count

C$j

D$num

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable not defined or incremented in the loop.

Using a variable that does not control the loop condition.

The variable $i is used in the loop and should be checked in the condition.

3fill in blank

hard

Fix the error in the do-while loop syntax by completing the missing part.

PHP

<?php
$i = 0;
do {
    echo $i . "\n";
    $i++;
} [1] ($i < 3);

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

Aif

Bdo

Cwhile

Dfor

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'do' again after the block instead of 'while'.

Using 'if' or 'for' which are not valid here.

The while keyword must follow the do-block to complete the do-while loop syntax.

4fill in blank

hard

Fill both blanks to create a do-while loop that prints numbers 1 to 3.

PHP

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

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

A++

B--

Cwhile

Ddo

Attempts:

3 left

💡 Hint

Common Mistakes

Using '--' to decrement instead of increment.

Using 'do' instead of 'while' after the block.

The variable $i is incremented with ++, and the loop ends with while keyword.

5fill in blank

hard

Fill all three blanks to create a do-while loop that prints even numbers from 2 to 6.

PHP

<?php
$num = 2;
do {
    echo $num . "\n";
    $num [1] 2;
} [2] ($num [3] 8);

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

A+=

Bwhile

C<

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '<' in the condition.

Using '+' instead of '+=' for increment.

The variable $num is increased by 2 using +=, the loop ends with while, and the condition checks if $num is less than 8.

Practice

1. What is the main difference between a do-while loop and a while loop in PHP?

easy

A. while loop always executes the code block at least once before checking the condition.

B. do-while loop executes the code block at least once before checking the condition.

C. do-while loop never checks the condition.

D. while loop executes the code block only if the condition is false.

Solution

1. Step 1: Understand the execution order of do-while loop

   A do-while loop runs the code block first, then checks the condition to decide if it should repeat.

2. Step 2: Compare with while loop behavior

   A while loop checks the condition first before running the code block, so it may not run at all if the condition is false initially.

3. Final Answer:

   do-while loop executes the code block at least once before checking the condition. -> Option B

4. Quick Check:

   do-while runs code once before condition check [OK]

Hint: Remember: do-while runs code first, then checks condition [OK]

Common Mistakes:

• Thinking while loop runs code before condition check
• Believing do-while skips condition check
• Confusing execution order of loops

2. Which of the following is the correct syntax for a do-while loop in PHP?

easy

A. do { /* code */ } while (condition);

B. do (condition) { /* code */ };

C. while (condition) { /* code */ } do;

D. do { /* code */ } until (condition);

Solution

1. Step 1: Recall PHP do-while syntax

   The correct syntax is: do { /* code */ } while (condition); with a semicolon after the while condition.

2. Step 2: Identify incorrect options

   Options A, C, and D use wrong keywords or misplaced parentheses, which are invalid in PHP.

3. Final Answer:

   do { /* code */ } while (condition); -> Option A

4. Quick Check:

   Correct do-while syntax ends with semicolon [OK]

Hint: Syntax: do { } while(condition); ends with semicolon [OK]

Common Mistakes:

• Omitting semicolon after while condition
• Using 'until' instead of 'while'
• Placing condition before code block

3. What will be the output of the following PHP code?

$i = 3;
do {
    echo $i . ' ';
    $i--;
} while ($i > 0);

medium

A. 3 2 1

B. 2 1 0

C. 3 2 1 0

D. 1 2 3

Solution

1. Step 1: Trace the loop iterations

   Initial value: $i = 3. Loop prints $i then decrements it. Iterations:
   1) print 3, $i=2
   2) print 2, $i=1
   3) print 1, $i=0

2. Step 2: Check loop condition after each iteration

   Loop continues while $i > 0. After printing 1, $i becomes 0, condition fails, loop stops.

3. Final Answer:

   3 2 1 -> Option A

4. Quick Check:

   Loop prints 3,2,1 then stops [OK]

Hint: do-while runs once before condition; count down from 3 [OK]

Common Mistakes:

• Including 0 in output
• Starting output from 1 instead of 3
• Confusing pre- and post-decrement

4. Identify the error in this PHP do-while loop:

$count = 1;
do {
    echo $count;
    $count++
} while ($count <= 3);

medium

A. Using do instead of while

B. Incorrect loop condition syntax

C. Missing semicolon after $count++

D. Variable $count not initialized

Solution

1. Step 1: Check each line for syntax errors

   The line $count++ is missing a semicolon at the end, which is required in PHP.

2. Step 2: Verify other parts of the loop

   The loop condition and variable initialization are correct. The use of do is proper for a do-while loop.

3. Final Answer:

   Missing semicolon after $count++ -> Option C

4. Quick Check:

   Every statement must end with semicolon [OK]

Hint: Check for missing semicolons inside loop [OK]

Common Mistakes:

• Forgetting semicolon after statements
• Misplacing loop condition parentheses
• Confusing do-while with while syntax

5. You want to read user input at least once and continue reading while the input is not empty. Which PHP do-while loop correctly implements this?

do {
    $input = trim(fgets(STDIN));
    // process input
} ???;

hard

A. while ($input !== '');

B. while ($input);

C. while ($input == '');

D. while (!empty($input));

Solution

1. Step 1: Understand the input condition

   We want to continue reading while input is not empty. The PHP function empty() returns true if input is empty.

2. Step 2: Choose the correct condition

   Using while (!empty($input)); means loop continues while input has some content, stopping when empty.

3. Final Answer:

   while (!empty($input)); -> Option D

4. Quick Check:

   Loop continues while input is not empty [OK]

Hint: Use while(!empty($input)) to loop until input is empty [OK]

Common Mistakes:

• Using equality to empty string incorrectly
• Using condition that stops loop too early
• Confusing empty() with isset()