Do-while loop execution model in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a do-while loop that prints "Hello" once.

C Sharp (C#)

do {
    Console.WriteLine("Hello");
} while ([1]);

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

Afalse

Btrue

C0

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'true' causes an infinite loop.

Using '0' or 'null' is invalid for a boolean condition.

The do-while loop runs the block once before checking the condition. Using false stops the loop after one iteration.

2fill in blank

medium

Complete the code to repeat the loop while the variable count is less than 3.

C Sharp (C#)

int count = 0;
do {
    Console.WriteLine(count);
    count++;
} while ([1]);

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

Acount > 3

Bcount >= 3

Ccount == 3

Dcount < 3

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'count > 3' causes the loop to never run.

Using 'count == 3' runs only when count equals 3, which is after the loop.

The loop continues while count is less than 3, printing 0, 1, and 2.

3fill in blank

hard

Fix the error in the do-while loop condition to compile correctly.

C Sharp (C#)

int i = 0;
do {
    Console.WriteLine(i);
    i++;
} while ([1]);

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

Ai < 5

Bi = 5

Ci++ < 5

Di => 5

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' assigns instead of compares.

Using '=>' is invalid syntax here.

The condition must be a boolean expression. i < 5 correctly checks if i is less than 5.

4fill in blank

hard

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

C Sharp (C#)

int num = 1;
do {
    Console.WriteLine(num);
    num[1]1;
} while (num [2] 4);

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

A++

B--

C<

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '--' decreases the number, causing an infinite loop.

Using '>' in the condition stops the loop immediately.

Increment num with ++ and loop while num < 4 to print 1, 2, 3.

5fill in blank

hard

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

C Sharp (C#)

int val = [1];
do {
    Console.WriteLine(val);
    val [2] 2;
} while (val [3] 8);

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

A2

B+=

C<

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' decreases the value, causing an infinite loop.

Using '>' in the condition stops the loop too early.

Start val at 2, add 2 each time with +=, and loop while val < 8 to print 2, 4, 6.

Practice

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

easy

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

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

C. The do-while loop never checks the condition.

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

Solution

1. Step 1: Understand do-while behavior

   The do-while loop runs the code block first, then checks the condition to decide if it repeats.

2. Step 2: Compare with while loop

   The while loop checks the condition first before running the code block, so it may not run at all.

3. Final Answer:

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

4. Quick Check:

   do-while runs 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 never checks condition
• Confusing the order of execution

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

easy

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

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

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

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

Solution

1. Step 1: Recall correct do-while syntax

   The do-while loop syntax is: do { /* code */ } while (condition);

2. Step 2: Identify incorrect options

   Options A, B, and D have incorrect order or missing parentheses/braces.

3. Final Answer:

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

4. Quick Check:

   Syntax: do { } while (condition); [OK]

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

Common Mistakes:

• Omitting semicolon after while condition
• Placing while before do
• Using parentheses incorrectly

3. What will be the output of the following C# code?

int count = 3;
do {
    Console.Write(count + " ");
    count--;
} while (count > 0);

medium

A. 1 2 3

B. 2 1 0

C. 3 2 1 0

D. 3 2 1

Solution

1. Step 1: Trace the loop execution

   Initial count is 3. The loop prints count, then decrements it. It repeats while count > 0.

2. Step 2: List printed values

   First iteration: prints 3, count becomes 2.
   Second: prints 2, count becomes 1.
   Third: prints 1, count becomes 0.
   Loop stops because count is not > 0.

3. Final Answer:

   3 2 1 -> Option D

4. Quick Check:

   Prints 3,2,1 then stops [OK]

Hint: Count down from 3, print before decrement, stop at zero [OK]

Common Mistakes:

• Including 0 in output
• Printing after decrement instead of before
• Confusing loop condition

4. Identify the error in the following do-while loop code snippet:

int i = 0;
do {
    Console.Write(i);
    i++;
} while i < 5;

medium

A. The variable i is not initialized.

B. The loop will never execute because condition is false.

C. Missing parentheses around the condition in the while statement.

D. The semicolon after the while condition is missing.

Solution

1. Step 1: Check syntax of while condition

   The condition in a do-while loop must be enclosed in parentheses: while (condition);

2. Step 2: Identify missing parentheses

   The code has while i < 5; without parentheses, causing a syntax error.

3. Final Answer:

   Missing parentheses around the condition in the while statement. -> Option C

4. Quick Check:

   Condition must be in parentheses [OK]

Hint: Always put condition inside parentheses after while [OK]

Common Mistakes:

• Forgetting parentheses around condition
• Missing semicolon after while statement
• Assuming variable initialization error

5. You want to write a do-while loop that asks the user to enter a positive number and repeats until the user enters a number greater than zero. Which code snippet correctly implements this?

hard

A. int num;
do {
Console.WriteLine("Enter a positive number:");
num = int.Parse(Console.ReadLine());
} while (num <= 0);

B. int num = 0;
do {
Console.WriteLine("Enter a positive number:");
num = int.Parse(Console.ReadLine());
} while (num > 0);

C. int num;
do {
Console.WriteLine("Enter a positive number:");
num = int.Parse(Console.ReadLine());
} while (num < 0);

D. int num = 1;
do {
Console.WriteLine("Enter a positive number:");
num = int.Parse(Console.ReadLine());
} while (num == 0);

Solution

1. Step 1: Understand the loop condition needed

   The loop should repeat while the number is not positive, i.e., while number is less than or equal to zero.

2. Step 2: Check each option's condition

   int num; do { Console.WriteLine("Enter a positive number:"); num = int.Parse(Console.ReadLine()); } while (num <= 0); uses while (num <= 0); which repeats until user enters a positive number.
   Other options have incorrect conditions that either stop too early or never repeat correctly.

3. Final Answer:

   int num; do { Console.WriteLine("Enter a positive number:"); num = int.Parse(Console.ReadLine()); } while (num <= 0); -> Option A

4. Quick Check:

   Repeat while number ≤ 0 to ensure positivity [OK]

Hint: Repeat while input ≤ 0 to ensure positive number [OK]

Common Mistakes:

• Using wrong comparison operators in condition
• Initializing variable incorrectly
• Stopping loop too early or never