Array methods (Sort, Reverse, IndexOf) in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this C# code using Array.Sort and Array.IndexOf?

Look at the code below. What will be printed to the console?

C Sharp (C#)

using System;

class Program {
    static void Main() {
        int[] numbers = {5, 3, 8, 1, 2};
        Array.Sort(numbers);
        int index = Array.IndexOf(numbers, 3);
        Console.WriteLine(index);
    }
}

A 1

B 3

C 2

D 0

💡 Hint

Remember that Array.Sort arranges the array in ascending order before searching.

After sorting, the array becomes [1, 2, 3, 5, 8]. The number 3 is at index 2 (0-based). So the output is 2.

❓ Predict Output

intermediate

What does this code print after reversing the array?

What will be the output of the following C# program?

C Sharp (C#)

using System;

class Program {
    static void Main() {
        string[] fruits = {"apple", "banana", "cherry"};
        Array.Reverse(fruits);
        Console.WriteLine(fruits[1]);
    }
}

A banana

B apple

C cherry

D IndexOutOfRangeException

💡 Hint

Think about how reversing changes the order of elements.

Original array: ["apple", "banana", "cherry"]. After reversing: ["cherry", "banana", "apple"]. The element at index 1 is "banana".

🔧 Debug

advanced

Why does this code throw an exception?

Examine the code below. It throws an exception when run. What is the cause?

C Sharp (C#)

using System;

class Program {
    static void Main() {
        int[] values = {10, 20, 30};
        Array.Reverse(values, 1, 5);
        Console.WriteLine(string.Join(",", values));
    }
}

A ArgumentOutOfRangeException because the length parameter exceeds array bounds

B NullReferenceException because the array is null

C InvalidOperationException because Reverse cannot be used on int arrays

D No exception, output is '10,30,20'

💡 Hint

Check the parameters passed to Array.Reverse carefully.

The method Array.Reverse(array, index, length) requires that index + length does not exceed the array length. Here, 1 + 5 = 6, which is greater than the array length 3, causing ArgumentOutOfRangeException.

❓ Predict Output

advanced

What is the output of this code using Array.IndexOf with a missing element?

What will this program print?

C Sharp (C#)

using System;

class Program {
    static void Main() {
        char[] letters = {'a', 'b', 'c', 'd'};
        int pos = Array.IndexOf(letters, 'z');
        Console.WriteLine(pos);
    }
}

A IndexOutOfRangeException

B -1

C 0

D 4

💡 Hint

What does Array.IndexOf return if the item is not found?

If the element is not found, Array.IndexOf returns -1.

🧠 Conceptual

expert

How many elements are in the array after these operations?

Consider this C# code snippet:

int[] arr = {4, 7, 1, 9};
Array.Sort(arr);
Array.Reverse(arr);
int index = Array.IndexOf(arr, 7);

After running this code, how many elements does arr contain?

A 0

B 3

C 1

D 4

💡 Hint

Sorting and reversing do not change the number of elements in the array.

The array arr starts with 4 elements. Sorting and reversing only change the order, not the size. So it still has 4 elements.