Array Deletion at Middle Index in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to shift elements left after deleting an element at index mid.

DSA C

for (int i = mid; i < n - 1; i++) {
    arr[i] = arr[1];
}

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

A[i + 1]

B[i - 1]

C[mid]

D[i]

Attempts:

3 left

💡 Hint

Common Mistakes

Using arr[i - 1] which shifts elements incorrectly.

Using arr[mid] which copies the same element repeatedly.

After deleting the element at index mid, each element from mid+1 to end shifts left by one, so arr[i] = arr[i + 1].

2fill in blank

medium

Complete the code to reduce the array size after deletion.

DSA C

n = n [1] 1;

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

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition which increases the size incorrectly.

Using multiplication or division which changes size wrongly.

After deleting one element, the size of the array decreases by 1, so n = n - 1.

3fill in blank

hard

Fix the error in the loop condition to avoid accessing out of bounds.

DSA C

for (int i = mid; i [1] n - 1; i++) {
    arr[i] = arr[i + 1];
}

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

A<=

B>=

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using <= causes out of bounds access.

Using > or >= causes the loop to skip or run incorrectly.

The loop should run while i is less than n - 1 to avoid accessing arr[n], so condition is i < n - 1.

4fill in blank

hard

Fill both blanks to print the array elements after deletion.

DSA C

for (int i = 0; i [1] n; i++) {
    printf("%d ", arr[2]);
}

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

A<

B<=

C[i]

D[n]

Attempts:

3 left

💡 Hint

Common Mistakes

Using <= causes printing one extra element.

Using arr[n] causes out of bounds access.

Loop runs from i = 0 to i < n, and prints arr[i] elements.

5fill in blank

hard

Fill all three blanks to delete the middle element and print the updated array.

DSA C

int mid = n [1] 2;
for (int i = mid; i < n [2] 1; i++) {
    arr[i] = arr[i [3] 1];
}
n = n - 1;
for (int i = 0; i < n; i++) {
    printf("%d ", arr[i]);
}

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

A/

B+

C-

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction instead of addition in arr[i] assignment.

Using multiplication or wrong loop condition.

mid is n / 2; loop runs while i < n - 1; arr[i] = arr[i + 1] to shift elements left.

Practice

1. What happens when you delete the middle element from an array of size 5?
int arr[5] = {10, 20, 30, 40, 50};
Delete the element at index 2 (middle). What is the new array?

easy

A. [10, 20, 40, 50]

B. [10, 20, 30, 40, 50]

C. [10, 20, 30, 50]

D. [20, 30, 40, 50]

Solution

1. Step 1: Identify the middle index and element

   The array has 5 elements, so the middle index is 2 (0-based). The element at index 2 is 30.

2. Step 2: Delete the middle element and shift remaining elements

   Remove 30, then shift elements after index 2 left by one: 40 moves to index 2, 50 moves to index 3.

3. Final Answer:

   [10, 20, 40, 50] -> Option A

4. Quick Check:

   Middle element removed, array size reduced by 1 [OK]

Hint: Remove middle, shift right elements left by one [OK]

Common Mistakes:

• Not shifting elements after deletion
• Deleting wrong index
• Leaving array size unchanged

2. Which of the following C code snippets correctly deletes the middle element from an array arr of size n?

easy

A. for (int i = n/2; i > 0; i--) arr[i] = arr[i - 1]; n--;

B. for (int i = 0; i < n/2; i++) arr[i] = arr[i + 1]; n--;

C. for (int i = n - 1; i > n/2; i--) arr[i] = arr[i - 1]; n--;

D. for (int i = n/2; i < n - 1; i++) arr[i] = arr[i + 1]; n--;

Solution

1. Step 1: Identify the middle index and loop direction

   The middle index is n/2 (integer division). To delete, shift elements after middle left.

2. Step 2: Check loop correctness

   for (int i = n/2; i < n - 1; i++) arr[i] = arr[i + 1]; n--; shifts elements from middle to end left by one, then reduces size. This is correct.

3. Final Answer:

   for (int i = n/2; i < n - 1; i++) arr[i] = arr[i + 1]; n--; -> Option D

4. Quick Check:

   Shift elements after middle left [OK]

Hint: Shift elements from middle to end left by one [OK]

Common Mistakes:

• Shifting elements before middle
• Looping in wrong direction
• Not reducing array size

3. What is the output of the following C code?

int arr[6] = {5, 10, 15, 20, 25, 30};
int n = 6;
int mid = n / 2;
for (int i = mid; i < n - 1; i++) {
    arr[i] = arr[i + 1];
}
n--;
for (int i = 0; i < n; i++) {
    printf("%d ", arr[i]);
}

medium

A. 5 10 15 20 25 30

B. 5 10 15 20 30

C. 5 10 15 25 30

D. 5 10 20 25 30

Solution

1. Step 1: Calculate middle index and deletion

   n=6, mid=3. Element at index 3 is 20. It will be deleted.

2. Step 2: Shift elements after index 3 left by one

   arr[3] = arr[4] (25), arr[4] = arr[5] (30), n becomes 5.

3. Step 3: Print updated array

   Elements: 5, 10, 15, 25, 30

4. Final Answer:

   5 10 15 25 30 -> Option C

5. Quick Check:

   Deleted middle element, shifted right elements left [OK]

Hint: Delete middle, shift right elements left, print first n-1 elements [OK]

Common Mistakes:

• Printing original array size
• Not shifting elements correctly
• Deleting wrong index

4. Find the error in this code snippet that deletes the middle element from an array arr of size n:

int mid = n / 2;
for (int i = 0; i < mid; i++) {
    arr[i] = arr[i + 1];
}
n--;

medium

A. Middle index calculation is wrong, should be (n-1)/2

B. Loop shifts elements before middle, should shift after middle

C. Array size decrement should be before loop

D. No error, code is correct

Solution

1. Step 1: Analyze loop range and shifting direction

   The loop runs from 0 to mid-1, shifting elements before middle left, which is incorrect.

2. Step 2: Correct shifting after middle index

   To delete middle element, shift elements from middle index to end left by one, not before middle.

3. Final Answer:

   Loop shifts elements before middle, should shift after middle -> Option B

4. Quick Check:

   Shift elements after middle, not before [OK]

Hint: Shift elements after middle, not before [OK]

Common Mistakes:

• Shifting elements before middle
• Wrong loop boundaries
• Not reducing array size

5. Given an array arr of size n where n is even, write the steps to delete the middle two elements and shift the rest. What will be the new array after deleting middle elements from {1, 2, 3, 4, 5, 6}?

hard

A. [1, 2, 5, 6]

B. [1, 2, 3, 6]

C. [1, 2, 4, 5, 6]

D. [1, 3, 4, 5, 6]

Solution

1. Step 1: Identify middle two indices for even-sized array

   For n=6, middle two indices are 2 and 3 (0-based), elements 3 and 4.

2. Step 2: Delete these two elements and shift remaining elements left

   Shift elements from index 4 and 5 left by two positions: 5 moves to index 2, 6 moves to index 3. Reduce size by 2.

3. Step 3: New array after deletion

   Array becomes [1, 2, 5, 6]

4. Final Answer:

   [1, 2, 5, 6] -> Option A

5. Quick Check:

   Delete two middle elements, shift right elements left by two [OK]

Hint: Delete two middles, shift right elements left by two [OK]

Common Mistakes:

• Deleting only one middle element
• Shifting elements incorrectly
• Not reducing array size by two