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

Practice - 5 Tasks

1fill in blank

easy

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

C Sharp (C#)

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

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

Acount >= 5

Bcount > 5

Ccount == 5

Dcount < 5

Attempts:

3 left

💡 Hint

Common Mistakes

Using > or >= instead of <

Using == which runs only when count equals 5

The while loop continues as long as the condition is true. To run while count is less than 5, use count < 5.

2fill in blank

medium

Complete the code to stop the while loop when number reaches 10.

C Sharp (C#)

int number = 0;
while (number [1] 10)
{
    Console.WriteLine(number);
    number++;
}

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

A>

B<

C>=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using > or >= which never becomes true at start

Using == which runs only once when number is 10

The loop should run while number is less than 10, so the condition is number < 10.

3fill in blank

hard

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

C Sharp (C#)

int i = 0;
while (i [1] 5)
{
    Console.WriteLine(i);
    // Missing increment
}

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

A>=

B>

C<

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using > which never becomes false if i starts at 0

Forgetting to increment i inside the loop

The condition should be i < 5 to run while i is less than 5. But the loop is missing i++ inside, which causes an infinite loop.

4fill in blank

hard

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

C Sharp (C#)

int num = 1;
while (num [1] 5)
{
    Console.WriteLine(num);
    num [2] 1;
}

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

A<=

B+=

C-=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using < instead of <= misses printing 5

Using -= 1 decreases the number causing infinite loop

The loop runs while num <= 5 to include 5. The increment uses num += 1 to add 1 each time.

5fill in blank

hard

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

C Sharp (C#)

int val = [1];
while (val [2] 10)
{
    Console.WriteLine(val);
    val [3] 2;
}

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

A2

B<=

C+=

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Starting at 1 prints odd numbers

Using < 10 misses printing 10

Using += 1 prints all numbers, not just even

Start at 2, run while val is less or equal to 10, and increase val by 2 each time to print even numbers.

Practice

1. What does a while loop do in C#?

easy

A. Stops the program immediately

B. Executes code only once regardless of condition

C. Repeats code a fixed number of times

D. Repeats a block of code as long as a condition is true

Solution

1. Step 1: Understand the purpose of a while loop

   A while loop runs repeatedly while its condition remains true.

2. Step 2: Compare with other options

   Options B, C, and D do not describe the behavior of a while loop correctly.

3. Final Answer:

   Repeats a block of code as long as a condition is true -> Option D

4. Quick Check:

   while loop = repeats while condition true [OK]

Hint: While loops run only if condition is true before each repeat [OK]

Common Mistakes:

• Thinking while loops run a fixed number of times
• Confusing while with do-while loops
• Assuming code runs at least once without checking condition

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

easy

A. while (condition) { /* code to repeat */ }

B. while condition { /* code to repeat */ }

C. while: (condition) { /* code to repeat */ }

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

Solution

1. Step 1: Recall correct while loop syntax

   The correct syntax requires parentheses around the condition and braces for the code block.

2. Step 2: Identify syntax errors in other options

   A has a colon after while, B misses parentheses around the condition, D has a semicolon after the condition making the loop body empty.

3. Final Answer:

   while (condition) { /* code to repeat */ } -> Option A

4. Quick Check:

   Correct syntax = while (condition) { /* code to repeat */ } [OK]

Hint: Always use parentheses for condition and braces for loop body [OK]

Common Mistakes:

• Omitting parentheses around condition
• Adding semicolon after while condition
• Using colon instead of parentheses

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

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

medium

A. 0 1 2 3

B. 3 2 1

C. 3 2 1 0

D. 1 2 3

Solution

1. Step 1: Trace the loop iterations

   count starts at 3, prints 3, then decrements to 2, prints 2, then 1, prints 1, then decrements to 0 and stops.

2. Step 2: Confirm output sequence

   The printed numbers are "3 2 1 " exactly in that order.

3. Final Answer:

   3 2 1 -> Option B

4. Quick Check:

   Loop prints count down from 3 to 1 [OK]

Hint: Count down loops print from start to 1 before stopping [OK]

Common Mistakes:

• Including 0 in output
• Printing numbers in ascending order
• Forgetting to decrement count

4. Identify the error in this code snippet:

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

medium

A. Missing braces causes only Console.Write(i) to loop, i++ runs once

B. Syntax error due to missing semicolon after while

C. Infinite loop because i is never incremented

D. No error, code runs correctly

Solution

1. Step 1: Analyze loop body without braces

   Only the first statement after while loops; here, only Console.Write(i) is inside the loop.

2. Step 2: Understand effect on i++

   i++ runs once after the loop finishes, so i never increments inside the loop, causing an infinite loop if braces were not considered.

3. Final Answer:

   Missing braces causes only Console.Write(i) to loop, i++ runs once -> Option A

4. Quick Check:

   Braces needed to include i++ in loop [OK]

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

Common Mistakes:

• Assuming both statements are inside loop without braces
• Thinking missing semicolon after while is error
• Confusing infinite loop cause

5. You want to read user input repeatedly until they type "exit". Which while loop correctly implements this in C#?

hard

A. while (true) {
string input = Console.ReadLine();
if (input != "exit") break;
}

B. string input;
do {
input = Console.ReadLine();
} while (input != "exit");

C. string input = Console.ReadLine();
while (input != "exit") {
input = Console.ReadLine();
}

D. string input;
while (input != "exit") {
input = Console.ReadLine();
}

Solution

1. Step 1: Understand the need to read input before loop

   We must read input once before the while condition to avoid skipping the first input.

2. Step 2: Check each option's logic

   string input = Console.ReadLine(); while (input != "exit") { input = Console.ReadLine(); } uses priming read pattern correctly. string input; do { input = Console.ReadLine(); } while (input != "exit"); is do-while, not while loop. while (true) { string input = Console.ReadLine(); if (input != "exit") break; } breaks incorrectly on non-exit input, stopping too early. string input; while (input != "exit") { input = Console.ReadLine(); } uses uninitialized input, compile error.

3. Final Answer:

   string input = Console.ReadLine(); while (input != "exit") { input = Console.ReadLine(); } -> Option C

4. Quick Check:

   Read input before while, then loop while not "exit" [OK]

Hint: Read input once before while to check condition correctly [OK]

Common Mistakes:

• Not reading input before while loop
• Using do-while instead of while
• Using infinite loop with break instead of while condition