Array Deletion at Middle Index in DSA C - Build from Scratch

Array Deletion at Middle Index

📖 Scenario: You have a list of daily temperatures recorded in an array. Sometimes, the middle day's temperature is incorrect and needs to be removed to keep the data accurate.

🎯 Goal: Build a program that deletes the middle element from an array of temperatures and shows the updated list.

📋 What You'll Learn

Create an integer array called temps with exactly 7 values: 23, 25, 22, 20, 24, 26, 21

Create an integer variable called size and set it to 7

Write code to delete the middle element (index 3) from the temps array by shifting elements left

Print the updated array elements separated by spaces

💡 Why This Matters

🌍 Real World

Deleting incorrect or unwanted data points from sensor readings or logs is common in data cleaning.

💼 Career

Understanding array manipulation is fundamental for software developers working with low-level data or embedded systems.

1

Create the temperature array

Create an integer array called temps with these exact values: 23, 25, 22, 20, 24, 26, 21.

DSA C

# Create the integer array temps with the given values
# Your code here

Hint

Use int temps[7] = {23, 25, 22, 20, 24, 26, 21}; to create the array.

2

Set the size variable

Create an integer variable called size and set it to 7.

DSA C

int temps[7] = {23, 25, 22, 20, 24, 26, 21};
# Create the integer variable size and set it to 7
# Your code here

Hint

Use int size = 7; to store the array length.

3

Delete the middle element

Write a for loop with variable i starting from 3 to size - 2 that shifts elements left in the temps array to delete the middle element at index 3. Then decrease size by 1.

DSA C

int temps[7] = {23, 25, 22, 20, 24, 26, 21};
int size = 7;
// Shift elements left to delete middle element at index 3
// Your code here

Hint

Use a for loop from 3 to size - 2 and assign temps[i] = temps[i + 1]; inside the loop. Then reduce size by 1.

4

Print the updated array

Write a for loop with variable i from 0 to size - 1 to print each element of temps separated by spaces.

DSA C

int temps[7] = {23, 25, 22, 20, 24, 26, 21};
int size = 7;
for (int i = 3; i < size - 1; i++) {
    temps[i] = temps[i + 1];
}
size--;
// Print the updated array elements separated by spaces
// Your code here

Hint

Use a for loop to print each element with printf("%d", temps[i]); and print a space after each except the last.

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