Jagged arrays in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Jagged Array Initialization

What is the output of the following C# code that initializes and prints a jagged array?

C Sharp (C#)

int[][] jagged = new int[2][];
jagged[0] = new int[] {1, 2};
jagged[1] = new int[] {3, 4, 5};

foreach (var arr in jagged)
{
    foreach (var num in arr)
    {
        Console.Write(num + " ");
    }
    Console.WriteLine();
}

A 1 2 \n3 4 5 \n

B 1 2 3 4 5 \n

C 3 4 5 \n1 2 \n

D 1 2 3 \n4 5 \n

💡 Hint

Remember that each element of a jagged array can have different lengths.

The jagged array has two inner arrays: the first with 2 elements (1,2) and the second with 3 elements (3,4,5). The nested loops print each inner array on its own line.

❓ Predict Output

intermediate

Accessing Jagged Array Elements

What value is printed by this C# code snippet?

C Sharp (C#)

int[][] jagged = new int[3][];
jagged[0] = new int[] {10};
jagged[1] = new int[] {20, 30};
jagged[2] = new int[] {40, 50, 60};

Console.WriteLine(jagged[1][1]);

A 20

B 40

C 30

D IndexOutOfRangeException

💡 Hint

Remember jagged arrays are arrays of arrays, so jagged[1] is the second inner array.

jagged[1] is the second inner array {20, 30}. Accessing index 1 of this array gives 30.

🔧 Debug

advanced

Identify the Error in Jagged Array Assignment

What error will this C# code produce when compiled or run?

C Sharp (C#)

int[][] jagged = new int[2][];
jagged[0] = new int[3];
jagged[1] = new int[2];
jagged[0][3] = 5;

A No error, runs successfully

B IndexOutOfRangeException at runtime

C NullReferenceException at runtime

D Compile-time error: invalid array index

💡 Hint

Check the valid indices for jagged[0] which has length 3.

jagged[0] has length 3, so valid indices are 0,1,2. Accessing index 3 causes IndexOutOfRangeException at runtime.

📝 Syntax

advanced

Correct Syntax for Jagged Array Declaration

Which option correctly declares and initializes a jagged array of integers with 2 inner arrays, the first with 1 element and the second with 2 elements?

A int[] jagged[] = new int[2][] { new int[1], new int[2] };

B int[,] jagged = new int[,] { {1}, {2, 3} };

C int[][] jagged = new int[2] { {1}, {2, 3} };

D int[][] jagged = new int[][] { new int[1], new int[2] };

💡 Hint

Jagged arrays use [][] notation and each inner array must be initialized separately.

Option D correctly declares a jagged array with two inner arrays of sizes 1 and 2. Option D uses a rectangular array syntax. Option D has invalid syntax mixing sizes and initializers. Option D has invalid declaration syntax.

🚀 Application

expert

Sum of All Elements in a Jagged Array

Given the jagged array below, what is the value of the variable 'total' after running the code?

C Sharp (C#)

int[][] jagged = new int[][] {
    new int[] {1, 2, 3},
    new int[] {4, 5},
    new int[] {6}
};

int total = 0;
foreach (var inner in jagged)
{
    foreach (var num in inner)
    {
        total += num;
    }
}

Console.WriteLine(total);

A 21

B 20

C 19

D 18

💡 Hint

Add all numbers: 1+2+3+4+5+6.

The sum is 1+2+3=6, plus 4+5=9, plus 6 = 6+9+6=21.