For loop execution model in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple for loop with increment

What is the output of the following C# code?

C Sharp (C#)

for (int i = 0; i < 3; i++)
{
    Console.Write(i);
}

A 012

B 123

C 321

D 0 1 2

💡 Hint

Remember the loop starts at 0 and runs while i is less than 3.

The loop starts at 0 and runs while i is less than 3, printing i each time without spaces. So it prints 0, then 1, then 2, resulting in '012'.

❓ Predict Output

intermediate

For loop with break statement output

What will be printed by this C# code?

C Sharp (C#)

for (int i = 0; i < 5; i++)
{
    if (i == 3) break;
    Console.Write(i);
}

A 012

B 01234

C 0123

D 345

💡 Hint

The loop stops when i equals 3.

The loop prints i starting from 0. When i reaches 3, the break stops the loop before printing 3. So output is '012'.

❓ Predict Output

advanced

For loop with multiple variables and complex condition

What is the output of this C# code snippet?

C Sharp (C#)

for (int i = 0, j = 5; i < j; i++, j--)
{
    Console.Write(i + j);
}

A 1010

B 57

C 59

D 555

💡 Hint

Add i and j each loop iteration and print the sum.

Loop runs while i < j. Iterations: 1) i=0, j=5 sum=5 2) i=1, j=4 sum=5 3) i=2, j=3 sum=5 After third iteration, i=3, j=2 stops loop. Output is '555'.

❓ Predict Output

advanced

For loop with continue statement effect

What will be the output of this C# code?

C Sharp (C#)

for (int i = 0; i < 5; i++)
{
    if (i % 2 == 0) continue;
    Console.Write(i);
}

A 1357

B 135

C 13

D 24

💡 Hint

The continue skips even numbers.

The loop skips printing when i is even (0,2,4). It prints only odd i values less than 5: 1 and 3. So output is '13'.

🧠 Conceptual

expert

Number of iterations in nested for loops

How many times will the innermost statement execute in this nested loop?

C Sharp (C#)

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

A 12

B 6

C 3

D 9

💡 Hint

Count how many times the inner loop runs for each i.

When i=1, j runs 1 to 3 → 3 times When i=2, j runs 2 to 3 → 2 times When i=3, j runs 3 to 3 → 1 time Total = 3 + 2 + 1 = 6 times.

Practice

1. What are the three main parts of a for loop in C#?

easy

A. Declaration, execution, and termination

B. Initialization, condition check, and increment/decrement

C. Start, middle, and end

D. Input, process, and output

Solution

1. Step 1: Understand the structure of a for loop

   A for loop has three parts inside parentheses: initialization, condition, and increment/decrement.

2. Step 2: Match parts to options

   Initialization sets the start value, condition checks if the loop continues, and increment/decrement changes the variable each time.

3. Final Answer:

   Initialization, condition check, and increment/decrement -> Option B

4. Quick Check:

   for loop parts = initialization, condition, increment [OK]

Hint: Remember: start, check, change in for loop [OK]

Common Mistakes:

• Confusing for loop parts with general program steps
• Thinking for loop has only two parts
• Mixing up condition and increment roles

2. Which of the following is the correct syntax for a basic for loop in C# that counts from 0 to 4?

easy

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

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

C. for (int i = 0; i < 4; i++) { }

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

Solution

1. Step 1: Check syntax correctness

   In C#, the for loop syntax requires parentheses around initialization, condition, and increment, and braces for the loop body.

2. Step 2: Validate each option

   for (int i = 0; i < 4; i++) { } only counts 0 to 3 (missing 4); for int i = 0; i < 5; i++ { } misses parentheses; for (int i = 0; i < 5; i++) { } is correct syntax counting 0 to 4; for (i = 0; i < 5; i++) { } misses type declaration for i.

3. Final Answer:

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

4. Quick Check:

   Correct for loop syntax uses parentheses and semicolons [OK]

Hint: Use parentheses and semicolons in for loop header [OK]

Common Mistakes:

• Omitting parentheses around for loop parts
• Missing type declaration for loop variable
• Using wrong comparison operators

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

for (int i = 1; i <= 3; i++)
{
    Console.Write(i + " ");
}

medium

A. 1 2 3

B. 0 1 2 3

C. 1 2 3 4

D. 3 2 1

Solution

1. Step 1: Analyze loop range

   The loop starts at i=1 and runs while i is less than or equal to 3, so it runs for i=1, 2, 3.

2. Step 2: Determine output per iteration

   Each iteration prints the current i followed by a space, so output is "1 ", "2 ", "3 ".

3. Final Answer:

   1 2 3 -> Option A

4. Quick Check:

   Loop prints 1 to 3 with spaces [OK]

Hint: Check loop start and end values carefully [OK]

Common Mistakes:

• Assuming loop starts at 0 instead of 1
• Including an extra number beyond the condition
• Printing in reverse order

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

for (int i = 0; i < 5; i++)
    Console.WriteLine(i);
    Console.WriteLine("Done");

medium

A. Infinite loop due to wrong condition

B. Syntax error: semicolon missing after for statement

C. Loop variable i is not declared

D. Missing braces causes only first line to loop

Solution

1. Step 1: Check loop body structure

   Without braces, only the first statement after for is inside the loop; the second statement runs once after the loop.

2. Step 2: Understand effect on output

   "Done" prints once after loop finishes, which might be unexpected if intended inside loop.

3. Final Answer:

   Missing braces causes only first line to loop -> Option D

4. Quick Check:

   Use braces to include multiple statements in loop [OK]

Hint: Use braces {} for multiple statements in loops [OK]

Common Mistakes:

• Assuming all lines are inside loop without braces
• Thinking semicolon is needed after for header
• Confusing variable declaration errors

5. You want to print all even numbers from 2 to 10 using a for loop in C#. Which loop header correctly achieves this?

hard

A. for (int i = 0; i < 10; i += 2)

B. for (int i = 1; i <= 10; i++) if (i % 2 == 0)

C. for (int i = 2; i <= 10; i += 2)

D. for (int i = 2; i < 10; i++) if (i % 2 == 0)

Solution

1. Step 1: Understand the goal

   We want to print even numbers from 2 to 10 inclusive, so loop variable should start at 2 and go up to 10.

2. Step 2: Check each option

   for (int i = 2; i <= 10; i += 2) increments by 2 starting at 2, so it prints 2,4,6,8,10. for (int i = 1; i <= 10; i++) if (i % 2 == 0) has a condition inside loop but header increments by 1; it works but is less efficient. for (int i = 0; i < 10; i += 2) starts at 0 and stops before 10, missing 10. for (int i = 2; i < 10; i++) if (i % 2 == 0) increments by 1 and stops before 10, missing 10.

3. Final Answer:

   for (int i = 2; i <= 10; i += 2) -> Option C

4. Quick Check:

   Increment by 2 from 2 to 10 for even numbers [OK]

Hint: Increment by 2 starting at 2 for even numbers [OK]

Common Mistakes:

• Using i++ and filtering inside loop instead of incrementing by 2
• Starting loop at 0 or 1 instead of 2
• Stopping loop before reaching 10