Array Insertion at Middle Index in DSA C# - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert a value at the middle index of the array.

DSA C#

int[] arr = {1, 2, 4, 5};
int middle = arr.Length / 2;
int value = 3;
int[] result = new int[arr.Length + 1];
for (int i = 0; i < middle; i++) {
    result[i] = arr[i];
}
result[middle] = [1];
for (int i = middle; i < arr.Length; i++) {
    result[i + 1] = arr[i];
}

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

Aarr[middle]

Bmiddle

Cvalue

Darr[value]

Attempts:

3 left

💡 Hint

Common Mistakes

Using arr[middle] instead of value inserts the old element again.

Using middle as a value inserts the index, not the value.

We insert the new value at the middle index, so we assign 'value' to result[middle].

2fill in blank

medium

Complete the code to calculate the middle index for insertion.

DSA C#

int[] arr = {10, 20, 30, 40, 50};
int middle = [1];
// middle should be the index to insert in the middle

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

Aarr.Length / 2

Barr.Length - 1

Carr.Length / 3

Darr.Length + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using arr.Length - 1 gives the last index, not the middle.

Using arr.Length + 1 is out of bounds.

The middle index is the length divided by 2, which gives the center position.

3fill in blank

hard

Fix the error in the loop that copies elements after the middle index.

DSA C#

for (int i = middle; i < arr.Length; i++) {
    result[i [1] 1] = arr[i];
}

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

A-

B+

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' shifts elements left, overwriting data.

Using '*' or '/' causes invalid indexing.

We add 1 to the index in result to shift elements right after insertion.

4fill in blank

hard

Fill both blanks to create a loop that copies elements before the middle index.

DSA C#

for (int i = 0; i [1] middle; i++) {
    result[i] = arr[2];
}

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

A<

B<=

C[i]

D[middle]

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' copies one extra element.

Using '[middle]' copies the wrong element repeatedly.

The loop runs while i is less than middle, copying arr[i] to result[i].

5fill in blank

hard

Fill all three blanks to create a method that inserts a value at the middle index of an array.

DSA C#

public static int[] InsertMiddle(int[] arr, int value) {
    int middle = arr.Length [1] 2;
    int[] result = new int[arr.Length [2] 1];
    for (int i = 0; i [3] middle; i++) {
        result[i] = arr[i];
    }
    result[middle] = value;
    for (int i = middle; i < arr.Length; i++) {
        result[i + 1] = arr[i];
    }
    return result;
}

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

A/

B+

C<

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' instead of '+' for new array size causes too small array.

Using '<=' in loop copies one extra element.

Divide length by 2 for middle, add 1 for new array size, and loop while i < middle.

Practice

1. What happens when you insert an element at the middle index of an array in C#?

easy

A. The array size decreases by one.

B. Elements after the middle index shift right to make space for the new element.

C. The new element replaces the element at the middle index without shifting.

D. The array elements remain unchanged.

Solution

1. Step 1: Understand array insertion behavior

   When inserting at the middle, elements from that index onward must move right to avoid overwriting.

2. Step 2: Effect on array size and elements

   The array size increases by one, and elements after the middle index shift right to make space.

3. Final Answer:

   Elements after the middle index shift right to make space for the new element. -> Option B

4. Quick Check:

   Insertion shifts elements right = A [OK]

Hint: Insertion shifts elements right from middle index [OK]

Common Mistakes:

• Thinking the array size decreases
• Replacing element without shifting
• Assuming no change in elements

2. Which of the following is the correct syntax to insert an element at the middle index of an array in C# (assuming you use a List<int> named 'numbers')?

easy

A. numbers.AddAtMiddle(10);

B. numbers.Add(10, numbers.Count / 2);

C. numbers.InsertAtMiddle(10);

D. numbers.Insert(numbers.Count / 2, 10);

Solution

1. Step 1: Identify List insertion method

   List<T> in C# uses Insert(index, value) to insert at any position.

2. Step 2: Calculate middle index and insert

   Middle index is numbers.Count / 2; so Insert(numbers.Count / 2, 10) inserts 10 at middle.

3. Final Answer:

   numbers.Insert(numbers.Count / 2, 10); -> Option D

4. Quick Check:

   Insert(index, value) syntax = B [OK]

Hint: Use Insert(index, value) with middle index [OK]

Common Mistakes:

• Using non-existent methods like AddAtMiddle
• Confusing Add and Insert parameters
• Wrong method names

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

List<int> nums = new List<int> {1, 2, 3, 4, 5};
nums.Insert(nums.Count / 2, 99);
Console.WriteLine(string.Join(", ", nums));

medium

A. 1, 2, 3, 99, 4, 5

B. 1, 2, 3, 4, 5, 99

C. 1, 2, 99, 3, 4, 5

D. 99, 1, 2, 3, 4, 5

Solution

1. Step 1: Calculate middle index

   nums.Count is 5, so middle index = 5 / 2 = 2.

2. Step 2: Insert 99 at index 2

   Original list: [1, 2, 3, 4, 5]. After insertion: [1, 2, 99, 3, 4, 5].

3. Final Answer:

   1, 2, 99, 3, 4, 5 -> Option C

4. Quick Check:

   Insert at index 2 shifts elements right = D [OK]

Hint: Middle index = Count/2; insert shifts elements right [OK]

Common Mistakes:

• Inserting at wrong index
• Appending instead of inserting
• Miscounting middle index

4. The following code tries to insert an element at the middle index of an array but does not insert properly. What is the issue and how to fix it?

int[] arr = {1, 2, 3, 4};
int middle = arr.Length / 2;
arr[middle] = 99;

medium

A. Error: Cannot insert in fixed-size array; use List<int> and Insert method.

B. No error; code works fine.

C. Error: Index out of range; middle index calculation is wrong.

D. Error: Assignment operator is invalid here.

Solution

1. Step 1: Understand array size and insertion

   Arrays in C# have fixed size; you cannot insert elements to increase size.

2. Step 2: Fix by using List<int> and Insert method

   Use List<int> which supports dynamic insertion with Insert(index, value).

3. Final Answer:

   Error: Cannot insert in fixed-size array; use List<int> and Insert method. -> Option A

4. Quick Check:

   Fixed-size arrays can't insert = A [OK]

Hint: Arrays fixed size; use List for insertion [OK]

Common Mistakes:

• Thinking assignment inserts element
• Misunderstanding array size limits
• Wrong index calculation assumption

5. You have an array of integers with an even length. You want to insert a new element exactly in the middle so that the array size increases by one and elements after the middle shift right. Which approach is best in C#?

hard

A. Use a List<int>, insert at middle index, then convert back to array if needed.

B. Directly assign the new element at middle index in the existing array.

C. Create a new array with size +1, copy elements before middle, insert new element, then copy remaining elements.

D. Use Array.Resize to increase size and then assign at middle index.

Solution

1. Step 1: Understand array limitations

   Arrays have fixed size; direct insertion is not possible without creating a new array.

2. Step 2: Use List for dynamic insertion

   List<int> allows insertion at any index easily; after insertion, convert back to array if needed.

3. Final Answer:

   Use a List<int>, insert at middle index, then convert back to array if needed. -> Option A

4. Quick Check:

   List supports insertion; arrays do not [OK]

Hint: Use List for easy insertion, then convert to array [OK]

Common Mistakes:

• Trying to assign directly in fixed array
• Using Array.Resize incorrectly
• Manually copying arrays without List