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

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print numbers from 1 to 3 using a nested loop.

C Sharp (C#)

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

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

Ai

B5

C3

Dj

Attempts:

3 left

💡 Hint

Common Mistakes

Using the outer loop variable 'i' as the inner loop limit causes incorrect output.

Setting the inner loop limit to 5 prints extra numbers.

The inner loop should run from 1 to 3 to print numbers 1, 2, and 3.

2fill in blank

medium

Complete the code to print a 3x3 grid of stars (*) using nested loops.

C Sharp (C#)

for (int row = 1; row <= 3; row++) {
    for (int col = 1; col <= [1]; col++) {
        Console.Write("*");
    }
    Console.WriteLine();
}

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

A5

Bcol

Crow

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using the outer loop variable 'row' as the inner loop limit causes inconsistent stars per row.

Setting the inner loop limit to 5 prints too many stars.

The inner loop must run 3 times to print 3 stars per row.

3fill in blank

hard

Fix the error in the nested loops to correctly print pairs of numbers.

C Sharp (C#)

for (int x = 1; x <= 2; x++) {
    for (int y = 1; y <= [1]; y++) {
        Console.WriteLine($"({x}, {y})");
    }
}

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

Ax

B2

C3

Dy

Attempts:

3 left

💡 Hint

Common Mistakes

Using the outer loop variable 'x' as the inner loop limit causes incorrect pairs.

Setting the inner loop limit to 3 prints extra pairs.

The inner loop should run 2 times to print pairs (1,1), (1,2), (2,1), (2,2).

4fill in blank

hard

Fill both blanks to create a nested loop that prints a multiplication table for 1 to 3.

C Sharp (C#)

for (int i = 1; i <= [1]; i++) {
    for (int j = 1; j <= [2]; j++) {
        Console.Write($"{i * j} ");
    }
    Console.WriteLine();
}

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

A3

B5

C4

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using different limits for the loops causes incomplete or extra rows/columns.

Setting limits higher than 3 prints a larger table than required.

Both loops should run from 1 to 3 to print a 3x3 multiplication table.

5fill in blank

hard

Fill all three blanks to create a nested loop that prints a right-angled triangle of stars.

C Sharp (C#)

for (int row = 1; row <= [1]; row++) {
    for (int col = 1; col <= [2]; col++) {
        if (col <= [3]) {
            Console.Write("*");
        }
    }
    Console.WriteLine();
}

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

A5

Brow

Ccol

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'col' instead of 'row' in the if condition prints incorrect patterns.

Setting different limits for loops causes uneven triangle shapes.

The outer and inner loops run 5 times. The if condition prints stars up to the current row number to form a triangle.

Practice

1. What happens when you use a nested loop in C#?

easy

A. Both loops run at the same time independently.

B. The outer loop runs only once and the inner loop runs multiple times.

C. The loops run only if a condition outside the loops is true.

D. The inner loop runs completely for each iteration of the outer loop.

Solution

1. Step 1: Understand nested loop structure

   In nested loops, the outer loop controls how many times the inner loop runs fully.

2. Step 2: Analyze loop execution order

   For each iteration of the outer loop, the inner loop runs from start to finish before the outer loop moves to the next iteration.

3. Final Answer:

   The inner loop runs completely for each iteration of the outer loop. -> Option D

4. Quick Check:

   Nested loops = inner loop runs fully each outer loop [OK]

Hint: Inner loop finishes all steps per outer loop step [OK]

Common Mistakes:

• Thinking both loops run simultaneously
• Assuming outer loop runs only once
• Confusing loop execution order

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

easy

A. for(int i = 0; i < 3; i++) { for(int j = 0; j < 2; j++) { Console.WriteLine(i + j); } }

B. for i in range(3) { for j in range(2) { Console.WriteLine(i + j); } }

C. for(int i = 0; i < 3; i++) for(int j = 0; j < 2; j++) Console.WriteLine(i + j); }

D. foreach(int i = 0; i < 3; i++) { foreach(int j = 0; j < 2; j++) { Console.WriteLine(i + j); } }

Solution

1. Step 1: Check C# for loop syntax

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

2. Step 2: Verify nested loop braces and statements

   for(int i = 0; i < 3; i++) { for(int j = 0; j < 2; j++) { Console.WriteLine(i + j); } } correctly nests two for loops with braces and valid syntax. Other options use incorrect syntax or keywords.

3. Final Answer:

   for(int i = 0; i < 3; i++) { for(int j = 0; j < 2; j++) { Console.WriteLine(i + j); } } -> Option A

4. Quick Check:

   C# for loop syntax = for(int i = 0; i < 3; i++) { for(int j = 0; j < 2; j++) { Console.WriteLine(i + j); } } [OK]

Hint: Remember C# for loop uses semicolons inside parentheses [OK]

Common Mistakes:

• Using Python-like syntax in C#
• Missing semicolons in for loop
• Using foreach incorrectly for numeric loops

3. What is the output of this C# code?

for(int i = 1; i <= 2; i++) {
  for(int j = 1; j <= 3; j++) {
    Console.Write(i * j + " ");
  }
  Console.WriteLine();
}

medium

A. 6 12

B. 1 2 3
2 4 6

C. 1 1 1
2 2 2

D. 1 2 3 4 5 6

Solution

1. Step 1: Trace outer loop values

   Outer loop i runs from 1 to 2 (two iterations).

2. Step 2: Calculate inner loop outputs per i

   For i=1, inner loop j=1 to 3 outputs 1*1=1, 1*2=2, 1*3=3. For i=2, inner loop outputs 2*1=2, 2*2=4, 2*3=6.

3. Final Answer:

   1 2 3 2 4 6 -> Option B

4. Quick Check:

   Nested loops multiply i and j = output lines [OK]

Hint: Multiply outer and inner loop counters for output [OK]

Common Mistakes:

• Confusing loop ranges
• Printing without spaces or newlines
• Mixing up i and j in multiplication

4. Identify the error in this nested loop code:

for(int i = 0; i < 3; i++) {
  for(int j = 0; j < 2; j++)
    Console.WriteLine(i + j);
  }
}

medium

A. Extra closing brace '}' after the inner loop.

B. Missing semicolon after Console.WriteLine statement.

C. Incorrect loop condition in the outer loop.

D. Variable j is not declared.

Solution

1. Step 1: Check braces matching

   There is an extra closing brace '}' after the inner loop which causes a syntax error.

2. Step 2: Verify other syntax elements

   Console.WriteLine has correct syntax, loops have valid conditions, and variables are declared properly.

3. Final Answer:

   Extra closing brace '}' after the inner loop. -> Option A

4. Quick Check:

   Brace mismatch = syntax error [OK]

Hint: Count opening and closing braces carefully [OK]

Common Mistakes:

• Ignoring extra or missing braces
• Assuming missing semicolon error
• Confusing variable declaration errors

5. You want to print a multiplication table from 1 to 3 using nested loops in C#. Which code correctly prints the table with rows and columns aligned?

hard

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

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

C. for(int i = 1; i <= 3; i++) { for(int j = 1; j <= 3; j++) { Console.Write($"{i*j,4}"); } Console.WriteLine(); }

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

Solution

1. Step 1: Understand formatting for aligned output

   Using Console.Write with format specifier {value,4} aligns numbers in columns with 4 spaces width.

2. Step 2: Check nested loop and output structure

   for(int i = 1; i <= 3; i++) { for(int j = 1; j <= 3; j++) { Console.Write($"{i*j,4}"); } Console.WriteLine(); } prints products in a grid with spaces, then moves to next line after inner loop finishes, creating a table.

3. Final Answer:

   for(int i = 1; i <= 3; i++) { for(int j = 1; j <= 3; j++) { Console.Write($"{i*j,4}"); } Console.WriteLine(); } -> Option C

4. Quick Check:

   Formatted nested loops print aligned multiplication table [OK]

Hint: Use Console.Write with alignment specifier for columns [OK]

Common Mistakes:

• Using Console.WriteLine inside inner loop causing new lines
• Not formatting output for alignment
• Missing Console.WriteLine after inner loop