Why loops are needed in C Sharp (C#) - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print numbers from 1 to 5 using a loop.

C Sharp (C#)

for (int i = 1; i [1] 5; i++)
{
    Console.WriteLine(i);
}

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

A<

B<=

C>

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using > or >= will not run the loop correctly.

Using < will exclude 5 from printing.

The loop should run while i is less than or equal to 5 to print numbers 1 to 5.

2fill in blank

medium

Complete the code to sum numbers from 1 to 10 using a loop.

C Sharp (C#)

int sum = 0;
for (int num = 1; num [1] 10; num++)
{
    sum += num;
}
Console.WriteLine(sum);

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

A<

B>=

C>

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using < will exclude 10 from the sum.

Using > or >= will cause the loop not to run as expected.

The loop should include 10, so use <= to sum numbers 1 through 10.

3fill in blank

hard

Fix the error in the loop condition to print all elements of the array.

C Sharp (C#)

string[] fruits = {"apple", "banana", "cherry"};
for (int i = 0; i [1] fruits.Length; i++)
{
    Console.WriteLine(fruits[i]);
}

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

A<=

B>

C<

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using <= causes an index out of range error.

Using > or >= will not enter the loop correctly.

Array indexes go from 0 to Length - 1, so the loop should run while i < fruits.Length.

4fill in blank

hard

Fill both blanks to create a loop that prints even numbers from 2 to 10.

C Sharp (C#)

for (int num = [1]; num [2] 10; num += 2)
{
    Console.WriteLine(num);
}

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

A2

B<

C<=

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Starting at 1 will print odd numbers.

Using < will exclude 10 from printing.

The loop starts at 2 and runs while num <= 10 to include 10.

5fill in blank

hard

Fill all three blanks to create a loop that prints numbers from 5 down to 1.

C Sharp (C#)

for (int i = [1]; i [2] 1; i [3])
{
    Console.WriteLine(i);
}

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

A5

B>=

C--

D++

Attempts:

3 left

💡 Hint

Common Mistakes

Using ++ will increase i and cause an infinite loop.

Using < instead of >= will skip printing 1.

The loop starts at 5, runs while i >= 1, and decreases i by 1 each time.

Practice

1. Why do we use loops in C# programming?

easy

A. To repeat a block of code multiple times automatically

B. To store multiple values in a single variable

C. To create new data types

D. To stop the program from running

Solution

1. Step 1: Understand the purpose of loops

   Loops are used to run the same code many times without writing it repeatedly.

2. Step 2: Identify the correct use case

   Repeating code automatically matches the description of loops.

3. Final Answer:

   To repeat a block of code multiple times automatically -> Option A

4. Quick Check:

   Loops repeat code [OK]

Hint: Loops repeat code to save time and effort [OK]

Common Mistakes:

• Confusing loops with variables
• Thinking loops create new data types
• Believing loops stop the program

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

easy

A. for i = 0 to 5 { }

B. for (int i = 0; i < 5; i++) { }

C. loop (int i = 0; i < 5; i++) { }

D. foreach (int i = 0; i < 5; i++) { }

Solution

1. Step 1: Recall C# for loop syntax

   The correct for loop uses parentheses with initialization, condition, and increment separated by semicolons.

2. Step 2: Compare options

   for (int i = 0; i < 5; i++) { } matches the correct syntax exactly.

3. Final Answer:

   for (int i = 0; i < 5; i++) { } -> Option B

4. Quick Check:

   Correct for loop syntax [OK]

Hint: For loops use semicolons inside parentheses [OK]

Common Mistakes:

• Using 'to' instead of semicolons
• Using 'loop' keyword instead of 'for'
• Confusing foreach with for loop syntax

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

int sum = 0;
for (int i = 1; i <= 3; i++)
{
    sum += i;
}
Console.WriteLine(sum);

medium

A. Error

B. 3

C. 0

D. 6

Solution

1. Step 1: Trace the loop iterations

   The loop runs with i = 1, 2, 3. sum adds 1 + 2 + 3.

2. Step 2: Calculate the sum

   sum = 0 + 1 = 1, then 1 + 2 = 3, then 3 + 3 = 6.

3. Final Answer:

   6 -> Option D

4. Quick Check:

   1+2+3 = 6 [OK]

Hint: Add numbers from 1 to 3 to get sum [OK]

Common Mistakes:

• Adding only the last number
• Starting loop from 0 incorrectly
• Confusing sum initialization

4. Identify the error in this C# loop code:

int i = 0;
while (i < 3)
{
    Console.WriteLine(i);
}

medium

A. Missing increment of i inside the loop

B. Incorrect while loop syntax

C. Console.WriteLine cannot be used inside loops

D. Variable i should be declared inside the loop

Solution

1. Step 1: Analyze the while loop behavior

   The loop condition is i < 3, but i never changes inside the loop.

2. Step 2: Identify the problem caused

   Without incrementing i, the loop runs forever (infinite loop).

3. Final Answer:

   Missing increment of i inside the loop -> Option A

4. Quick Check:

   Infinite loop due to no i++ [OK]

Hint: Always update loop variable to avoid infinite loops [OK]

Common Mistakes:

• Forgetting to increment loop variable
• Thinking syntax is wrong when it's correct
• Believing Console.WriteLine is invalid inside loops

5. You want to print all even numbers from 2 to 10 using a loop in C#. Which code snippet correctly does this?

hard

A. while (int i = 2; i <= 10; i++) { Console.WriteLine(i); }

B. for (int i = 1; i <= 10; i++) { if (i % 2 == 1) Console.WriteLine(i); }

C. for (int i = 2; i <= 10; i += 2) { Console.WriteLine(i); }

D. do { Console.WriteLine(i); i += 2; } while (i < 2);

Solution

1. Step 1: Understand the goal

   We want to print even numbers from 2 to 10 inclusive.

2. Step 2: Check each option

   for (int i = 2; i <= 10; i += 2) { Console.WriteLine(i); } starts at 2, increments by 2, and prints each value up to 10, which is correct.

3. Final Answer:

   for (int i = 2; i <= 10; i += 2) { Console.WriteLine(i); } -> Option C

4. Quick Check:

   Increment by 2 from 2 to 10 [OK]

Hint: Increment by 2 to print even numbers [OK]

Common Mistakes:

• Printing odd numbers instead of even
• Incorrect while loop syntax
• Wrong loop condition causing no output