Multi-dimensional arrays in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a multi-dimensional array in C#?

A multi-dimensional array is an array with more than one dimension, like a table with rows and columns. It stores data in a grid-like structure.

beginner

How do you declare a 2D array of integers with 3 rows and 4 columns in C#?

You declare it like this: <br>int[,] array = new int[3,4];<br>This creates a grid with 3 rows and 4 columns.

beginner

How do you access the element in the 2nd row and 3rd column of a 2D array named array?

Use array[1, 2] because indexing starts at 0. So row 2 is index 1, column 3 is index 2.

intermediate

What is the difference between a rectangular array and a jagged array in C#?

A rectangular array has rows and columns all the same size (like a grid). A jagged array is an array of arrays where each row can have different lengths.

beginner

How can you loop through all elements of a 2D array in C#?

Use two nested loops: one for rows and one for columns. For example:<br>for (int i = 0; i < rows; i++) {<br> for (int j = 0; j < cols; j++) {<br> // access array[i, j]<br> }<br>}

How do you declare a 3D array of doubles with dimensions 2x3x4 in C#?

A double arr = new double[2,3,4];

B double[][][] arr = new double[2][3][4];

C double[] arr = new double[2,3,4];

D double[,,] arr = new double[2,3,4];

In C#, multi-dimensional arrays use commas inside square brackets. So double[,,] declares a 3D array.

What is the index of the first element in any dimension of a C# array?

A -1

B 1

C 0

D Depends on the array

C# arrays are zero-indexed, so the first element is always at index 0.

Which of these is a jagged array declaration in C#?

A int[] jagged = new int[3,4];

B int[][] jagged = new int[3][];

C int[,] jagged = new int[3,4,5];

D int jagged = new int[3][];

Jagged arrays are arrays of arrays, declared with multiple square brackets like int[][].

How do you find the number of rows in a 2D array named arr?

A arr.GetLength(0)

B arr.GetLength(1)

C arr.Length

D arr.Rank

GetLength(0) returns the size of the first dimension (rows) in a multi-dimensional array.

What will happen if you try to access array[3,0] in a 3x4 array?

A Throws an IndexOutOfRangeException

B Returns the first element

C Returns null

D Returns default value 0

Index 3 is out of range for rows (0 to 2), so it throws an exception.

Explain how to declare, initialize, and access elements in a 2D array in C#.

Think of a table with rows and columns.

Describe the difference between rectangular and jagged arrays and when you might use each.

Imagine a perfect grid vs. uneven shelves.