Array methods (Sort, Reverse, IndexOf) in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to sort the array in ascending order.

C Sharp (C#)

int[] numbers = {5, 3, 8, 1};
Array.[1](numbers);

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

AIndexOf

BReverse

CSort

DFind

Attempts:

3 left

💡 Hint

Common Mistakes

Using Reverse instead of Sort will flip the array but not sort it.

IndexOf is used to find an element, not to sort.

The Array.Sort method sorts the array elements in ascending order.

2fill in blank

medium

Complete the code to reverse the order of elements in the array.

C Sharp (C#)

string[] fruits = {"apple", "banana", "cherry"};
Array.[1](fruits);

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

AReverse

BSort

CIndexOf

DClear

Attempts:

3 left

💡 Hint

Common Mistakes

Using Sort will reorder elements, not reverse them.

IndexOf is for searching, not changing order.

The Array.Reverse method reverses the order of elements in the array.

3fill in blank

hard

Fix the error in the code to find the index of the element "dog" in the array.

C Sharp (C#)

string[] animals = {"cat", "dog", "bird"};
int index = Array.[1](animals, "dog");

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

ASort

BFindIndex

CReverse

DIndexOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using Sort or Reverse will not find an element's index.

FindIndex is a method for lists, not arrays.

The Array.IndexOf method returns the index of the specified element in the array.

4fill in blank

hard

Fill both blanks to sort the array and then reverse it.

C Sharp (C#)

int[] values = {4, 7, 2, 9};
Array.[1](values);
Array.[2](values);

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

ASort

BClear

CReverse

DIndexOf

Attempts:

3 left

💡 Hint

Common Mistakes

Reversing before sorting will not produce descending order.

Using Clear or IndexOf here is incorrect.

First, Sort arranges the array in ascending order. Then, Reverse flips it to descending order.

5fill in blank

hard

Fill all three blanks to find the index of "blue" in the colors array after sorting and reversing it.

C Sharp (C#)

string[] colors = {"red", "blue", "green"};
Array.[1](colors);
Array.[2](colors);
int pos = Array.[3](colors, "blue");

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

ASort

BIndexOf

CReverse

DClear

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to find the index before sorting and reversing.

Using Clear instead of Reverse or IndexOf.

First, Sort orders the array. Then, Reverse flips it. Finally, IndexOf finds the position of "blue".

Practice

1. What does the Array.Sort method do to an array in C#?

easy

A. It reverses the order of the items.

B. It arranges the items in ascending order.

C. It finds the index of a specific item.

D. It removes duplicate items from the array.

Solution

1. Step 1: Understand Array.Sort purpose

   The Array.Sort method organizes the elements of an array in ascending order by default.

2. Step 2: Compare with other methods

   Array.Reverse flips the array, and Array.IndexOf finds an element's position, so they do different things.

3. Final Answer:

   It arranges the items in ascending order. -> Option B

4. Quick Check:

   Array.Sort = ascending order [OK]

Hint: Sort means arrange from smallest to largest [OK]

Common Mistakes:

• Confusing Sort with Reverse
• Thinking Sort finds an element's position
• Assuming Sort removes duplicates

2. Which of the following is the correct way to reverse an array named numbers in C#?

easy

A. numbers.Reverse();

B. numbers.ReverseArray();

C. Array.Sort(numbers);

D. Array.Reverse(numbers);

Solution

1. Step 1: Identify correct method call syntax

   In C#, Array.Reverse is a static method that takes the array as an argument, so Array.Reverse(numbers); is correct.

2. Step 2: Check other options

   numbers.Reverse() is a LINQ extension returning IEnumerable, not reversing in place. Array.Sort sorts, not reverses. ReverseArray() does not exist.

3. Final Answer:

   Array.Reverse(numbers); -> Option D

4. Quick Check:

   Reverse array = Array.Reverse(array) [OK]

Hint: Use Array.Reverse(array) to flip order [OK]

Common Mistakes:

• Using instance method Reverse() which doesn't reverse in place
• Confusing Sort with Reverse
• Calling non-existent methods

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

string[] fruits = {"apple", "banana", "cherry"};
Array.Sort(fruits);
Array.Reverse(fruits);
Console.WriteLine(fruits[0]);

medium

A. cherry

B. banana

C. apple

D. Runtime error

Solution

1. Step 1: Sort the array

   After Array.Sort(fruits);, the array becomes ["apple", "banana", "cherry"] (already sorted).

2. Step 2: Reverse the array

   After Array.Reverse(fruits);, the array becomes ["cherry", "banana", "apple"].

3. Step 3: Print first element

   fruits[0] is now "cherry".

4. Final Answer:

   cherry -> Option A

5. Quick Check:

   Sort then Reverse = descending order [OK]

Hint: Sort then Reverse = descending order, first item is largest [OK]

Common Mistakes:

• Assuming array stays sorted ascending
• Confusing Reverse with Sort
• Expecting runtime error due to method calls

4. The following code throws an error. What is the mistake?

int[] nums = {3, 1, 4};
nums.Sort();
Console.WriteLine(nums[0]);

medium

A. Arrays don't have a Sort() instance method.

B. The array must be reversed before sorting.

C. You must use Console.WriteLine(nums.Sort()); instead.

D. The array must be converted to a list before sorting.

Solution

1. Step 1: Identify method call error

   Arrays in C# do not have an instance method called Sort(). Sorting is done via the static method Array.Sort(array).

2. Step 2: Understand correct usage

   The correct way is Array.Sort(nums); to sort the array in place.

3. Final Answer:

   Arrays don't have a Sort() instance method. -> Option A

4. Quick Check:

   Use Array.Sort(array), not array.Sort() [OK]

Hint: Array.Sort is static; no instance Sort() method [OK]

Common Mistakes:

• Calling Sort() directly on array instance
• Confusing List.Sort() with Array.Sort()
• Trying to print Sort() return value

5. Given the array int[] values = {5, 3, 8, 3, 9};, which code snippet finds the index of the first occurrence of the number 3 and then reverses the array?

hard

A. int index = Array.FindIndex(values, 3);
Array.Sort(values);

B. int index = values.IndexOf(3);
Array.Reverse(values);

C. int index = Array.IndexOf(values, 3);
Array.Reverse(values);

D. int index = Array.IndexOf(values, 3);
Array.Sort(values);

Solution

1. Step 1: Find index of first 3

   Array.IndexOf(values, 3) correctly returns the first index where 3 appears, which is 1.

2. Step 2: Reverse the array

   Array.Reverse(values); reverses the array in place as required.

3. Final Answer:

   int index = Array.IndexOf(values, 3); Array.Reverse(values); -> Option C

4. Quick Check:

   IndexOf + Reverse = int index = Array.IndexOf(values, 3); Array.Reverse(values); [OK]

Hint: Use Array.IndexOf(array, value) to find index [OK]

Common Mistakes:

• Using instance method IndexOf on array (not valid)
• Confusing FindIndex with IndexOf
• Sorting instead of reversing