Multi-dimensional arrays in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a 2D array of integers with 3 rows and 4 columns.

C Sharp (C#)

int[,] matrix = new int[[1], 4];

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

A3

B4

C5

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing rows and columns sizes.

Using a single-dimensional array syntax.

The first dimension is the number of rows, which is 3 here.

2fill in blank

medium

Complete the code to assign the value 10 to the element in the second row and third column of the 2D array.

C Sharp (C#)

matrix[[1], 2] = 10;

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

A3

B1

C2

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 2 instead of 1 for the second row index.

Confusing row and column indices.

Array indices start at 0, so the second row is index 1.

3fill in blank

hard

Fix the error in the code to correctly declare and initialize a 2D array with 2 rows and 3 columns filled with zeros.

C Sharp (C#)

int[,] grid = new int[[1], 3];

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

A2

B0

C3

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 3 instead of 2 for the number of rows.

Using zero or one as the first dimension size.

The array should have 2 rows and 3 columns, so the first dimension is 2.

4fill in blank

hard

Fill both blanks to create a nested loop that prints all elements of a 2D array named 'data'.

C Sharp (C#)

for (int i = 0; i < data.GetLength([1]); i++) {
    for (int j = 0; j < data.GetLength([2]); j++) {
        Console.WriteLine(data[i, j]);
    }
}

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

A0

B1

C2

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the dimension indices.

Using invalid dimension numbers like 2 or 3.

GetLength(0) returns the number of rows, GetLength(1) returns the number of columns.

5fill in blank

hard

Fill all three blanks to create a 2D array 'table' with 2 rows and 3 columns, assign 5 to the first element, and print it.

C Sharp (C#)

int[,] table = new int[[1], [2]];
table[0, 0] = [3];
Console.WriteLine(table[0, 0]);

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

A3

B5

C2

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping rows and columns in the declaration.

Assigning the wrong value to the first element.

The array has 2 rows and 3 columns, so dimensions are 2 and 3. The value 5 is assigned to the first element.

Practice

1. What is a multi-dimensional array in C#?

easy

A. An array that can only hold one value

B. An array that stores only strings

C. An array with more than one dimension, like rows and columns

D. A list of unrelated variables

Solution

1. Step 1: Understand array dimensions

   A multi-dimensional array stores data in multiple dimensions, such as rows and columns, unlike a simple one-dimensional array.

2. Step 2: Recognize the definition

   An array with more than one dimension, like rows and columns correctly describes a multi-dimensional array as having more than one dimension, like a table with rows and columns.

3. Final Answer:

   An array with more than one dimension, like rows and columns -> Option C

4. Quick Check:

   Multi-dimensional array = rows and columns [OK]

Hint: Think of a table with rows and columns [OK]

Common Mistakes:

• Confusing multi-dimensional arrays with simple lists
• Thinking arrays can only hold one type of data
• Believing multi-dimensional arrays are unrelated variables

2. Which of the following is the correct way to declare a 2x3 multi-dimensional array of integers in C#?

easy

A. int[,] arr = new int[2,3];

B. int[][] arr = new int[2][3];

C. int arr[2,3];

D. int arr = new int[2,3];

Solution

1. Step 1: Recall C# multi-dimensional array syntax

   In C#, a 2D array is declared with commas inside square brackets: int[,] arr = new int[rows, columns];

2. Step 2: Check each option

   int[,] arr = new int[2,3]; uses correct syntax. int[][] arr = new int[2][3]; is jagged array syntax, not multi-dimensional. Options A and C are invalid syntax.

3. Final Answer:

   int[,] arr = new int[2,3]; -> Option A

4. Quick Check:

   Use comma inside brackets for multi-dimensional arrays [OK]

Hint: Use comma inside brackets for multi-dimensional arrays [OK]

Common Mistakes:

• Using jagged array syntax instead of multi-dimensional
• Missing 'new' keyword or wrong brackets
• Confusing array declaration with other languages

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

int[,] matrix = { {1, 2, 3}, {4, 5, 6} };
Console.WriteLine(matrix[1, 2]);

medium

A. 3

B. 5

C. Runtime error

D. 6

Solution

1. Step 1: Understand array indexing

   matrix[1, 2] means row 1, column 2. Rows and columns start at 0.

2. Step 2: Locate the value at matrix[1, 2]

   Row 1 is {4, 5, 6}, column 2 is the third element, which is 6.

3. Final Answer:

   6 -> Option D

4. Quick Check:

   matrix[1,2] = 6 [OK]

Hint: Remember indexing starts at zero for rows and columns [OK]

Common Mistakes:

• Confusing row and column indexes
• Starting count from 1 instead of 0
• Expecting the value 3 or 5 instead of 6

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

int[,] grid = new int[3, 3];
grid[3, 0] = 10;

medium

A. Index out of range error at grid[3, 0]

B. Syntax error in array declaration

C. Missing initialization of array

D. No error, code runs fine

Solution

1. Step 1: Check array size and valid indexes

   The array grid has size 3x3, so valid row indexes are 0, 1, 2.

2. Step 2: Analyze the assignment grid[3, 0]

   Index 3 for row is out of range, causing an IndexOutOfRangeException at runtime.

3. Final Answer:

   Index out of range error at grid[3, 0] -> Option A

4. Quick Check:

   Index 3 invalid for size 3 array [OK]

Hint: Indexes start at 0, max index is size-1 [OK]

Common Mistakes:

• Using index equal to array size
• Confusing syntax error with runtime error
• Assuming arrays auto-expand on invalid index

5. Given a 3x3 multi-dimensional array int[,] board representing a tic-tac-toe game, which code snippet correctly counts how many cells contain the value 1?

int count = 0;
// Which loop is correct?
A) for (int i = 0; i < 3; i++)
   for (int j = 0; j < 3; j++)
       if (board[i, j] == 1) count++;

B) for (int i = 1; i <= 3; i++)
   for (int j = 1; j <= 3; j++)
       if (board[i, j] == 1) count++;

C) for (int i = 0; i < 3; i++)
   for (int j = 0; j < 2; j++)
       if (board[i, j] == 1) count++;

D) for (int i = 0; i < 3; i++)
   for (int j = 0; j < 3; j++)
       if (board[j, i] == 1) count++;

hard

A. rorre egnar fo tuo xedni sesuaC

B. Causes index out of range error

C. Misses last column in counting

D. Counts transposed cells, not original positions

Solution

1. Step 1: Understand array indexing and loop ranges

   Indexes start at 0 and go up to size-1, so loops must run from 0 to less than 3.

2. Step 2: Analyze each option's loops

   Causes index out of range error correctly counts all cells with value 1 loops correctly over all rows and columns. Causes index out of range error causes index out of range error uses 1 to 3, causing out of range. Misses last column in counting misses last column by looping j to 2. Counts transposed cells, not original positions swaps indexes, counting transposed cells.

3. Final Answer:

   Causes index out of range error -> Option B

4. Quick Check:

   Loop from 0 to less than size for rows and columns [OK]

Hint: Loop indexes from 0 to size-1 for all dimensions [OK]

Common Mistakes:

• Starting loops at 1 instead of 0
• Using wrong loop limits causing missed elements
• Swapping row and column indexes accidentally