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

Recall & Review

beginner

What is a jagged array in C#?

A jagged array is an array of arrays, where each inner array can have a different length. It allows storing rows of different sizes, unlike a rectangular (multidimensional) array.

beginner

How do you declare a jagged array of integers with 3 rows in C#?

You declare it like this: <br>int[][] jaggedArray = new int[3][];<br>This creates an array with 3 elements, each of which can point to an integer array of any length.

beginner

How do you initialize the second row of a jagged array to have 4 elements?

You assign a new array to the second row like this:<br>jaggedArray[1] = new int[4];<br>This sets the second row to hold 4 integers.

beginner

How do you access the third element of the first row in a jagged array?

You use two indexes:<br>jaggedArray[0][2]<br>The first index selects the row, the second index selects the element in that row.

intermediate

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

A jagged array is an array of arrays where each inner array can have different lengths.<br>A multidimensional array is a single block of memory with fixed size in each dimension.<br>Jagged arrays offer more flexibility in row sizes.

How do you declare a jagged array with 5 rows in C#?

A int[][] arr = new int[5][];

B int[] arr = new int[5,5];

C int[] arr = new int[5];

D int[][] arr = new int[][];

Option A correctly declares a jagged array with 5 rows, each row can have different lengths.

Which syntax accesses the 2nd element of the 3rd row in a jagged array named 'jagged'?

A jagged[2][1]

B jagged[2,1]

C jagged[3][2]

D jagged[1][2]

Indexes start at 0, so the 3rd row is index 2 and the 2nd element is index 1.

Can jagged arrays have rows of different lengths?

A Only if using special syntax.

B No, all rows must have the same length.

C Only if declared as multidimensional arrays.

D Yes, each row can have a different length.

Jagged arrays are designed to allow rows of different lengths.

What happens if you try to access an element in a jagged array row that has not been initialized?

A It returns zero by default.

B You get a NullReferenceException.

C It automatically initializes the row.

D It throws a compile-time error.

If the inner array is null (not initialized), accessing it causes a NullReferenceException.

Which of these is a correct way to initialize a jagged array with 2 rows, first with 3 elements and second with 2 elements?

A int[] jagged = new int[2,3];

B int[][] jagged = new int[2][3];

C int[][] jagged = new int[2][]; jagged[0] = new int[3]; jagged[1] = new int[2];

D int[][] jagged = { new int[3], new int[2] };

Option C correctly declares the jagged array and initializes each row with different lengths.

Explain what a jagged array is and how it differs from a multidimensional array in C#.

Think about rows and their lengths.

Describe how to declare, initialize, and access elements in a jagged array in C#.

Remember jagged arrays are arrays of arrays.