Array Insertion at Middle Index in DSA C++ - Build from Scratch

Array Insertion at Middle Index

📖 Scenario: You are managing a list of daily temperatures recorded in a small weather station. Sometimes, a new temperature reading arrives late and needs to be inserted exactly in the middle of the existing list to keep the order balanced.

🎯 Goal: Build a program that inserts a new temperature value exactly at the middle index of an existing array of temperatures.

📋 What You'll Learn

Create an integer array called temperatures with exactly 5 values: 23, 25, 22, 24, 26

Create an integer variable called new_temp and set it to 27

Insert new_temp into the temperatures array exactly at the middle index (index 2)

Print the updated array elements separated by spaces

💡 Why This Matters

🌍 Real World

Inserting data in the middle of arrays is common in real-time data processing, like updating sensor readings or managing ordered lists.

💼 Career

Understanding array manipulation is fundamental for software developers working with low-level data structures, embedded systems, or performance-critical applications.

1

Create the initial array

Create an integer array called temperatures with these exact values: 23, 25, 22, 24, 26

DSA C++

# Your code here

Hint

Use a fixed size array with 6 elements to allow space for insertion later.

2

Add the new temperature variable

Create an integer variable called new_temp and set it to 27

DSA C++

int temperatures[6] = {23, 25, 22, 24, 26};
# Your code here

Hint

Just declare a simple integer variable for the new temperature.

3

Insert the new temperature at the middle index

Shift the elements from index 2 to the right by one position in the temperatures array, then insert new_temp at index 2

DSA C++

int temperatures[6] = {23, 25, 22, 24, 26};
int new_temp = 27;
// Your code here

Hint

Start shifting from the last element to avoid overwriting values.

4

Print the updated array

Use a for loop with variable i from 0 to 5 to print each element of temperatures separated by spaces

DSA C++

int temperatures[6] = {23, 25, 22, 24, 26};
int new_temp = 27;
for (int i = 5; i > 2; i--) {
    temperatures[i] = temperatures[i - 1];
}
temperatures[2] = new_temp;
// Your code here

Hint

Print all 6 elements with a space after each number.

Practice

1. What does inserting an element at the middle index of an array mean?

easy

A. Adding a new element exactly in the center, shifting others right

B. Replacing the middle element with a new one

C. Adding a new element at the end of the array

D. Removing the middle element from the array

Solution

1. Step 1: Understand middle index insertion

   Inserting at the middle means placing a new element at the center position, pushing existing elements right.

2. Step 2: Differentiate from other operations

   Replacing or removing elements is not insertion; adding at the end is not middle insertion.

3. Final Answer:

   Adding a new element exactly in the center, shifting others right -> Option A

4. Quick Check:

   Middle insertion means insert and shift right [OK]

Hint: Middle insertion shifts elements right from center [OK]

Common Mistakes:

• Thinking insertion replaces the middle element
• Confusing insertion with appending at the end
• Assuming middle means removing element

2. Which of the following C++ code snippets correctly inserts an element `x` at the middle index of array `arr` of size `n`?

easy

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

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

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

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

Solution

1. Step 1: Shift elements right from middle index

   Loop from end (n) down to middle (n/2 + 1) shifting elements right to make space.

2. Step 2: Insert element at middle index

   Assign new element x at index n/2 after shifting.

3. Final Answer:

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

4. Quick Check:

   Shift right then insert at middle [OK]

Hint: Shift elements right from end to middle before insert [OK]

Common Mistakes:

• Shifting elements left instead of right
• Inserting before shifting elements
• Incorrect loop direction causing overwrite

3. What is the output array after inserting 99 at the middle index of arr = {10, 20, 30, 40, 50} using the correct insertion method?

medium

A. [10, 20, 30, 40, 99, 50]

B. [10, 20, 99, 30, 40, 50]

C. [10, 20, 30, 99, 40, 50]

D. [10, 20, 30, 40, 50, 99]

Solution

1. Step 1: Calculate middle index

   Array size n=5, middle index = n/2 = 2 (0-based indexing).

2. Step 2: Shift elements right and insert 99

   Shift elements from index 4 to 2 right by one position, then insert 99 at index 2.

3. Final Answer:

   [10, 20, 99, 30, 40, 50] -> Option B

4. Quick Check:

   Insert at index 2 shifts right [OK]

Hint: Middle index = size/2; shift right, then insert [OK]

Common Mistakes:

• Inserting at wrong index (like 3 or 4)
• Not shifting elements before insertion
• Appending at the end instead of middle

4. Identify the error in the following code snippet that inserts element `x` at the middle index of array `arr` of size `n`:

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

medium

A. Loop shifts elements left instead of right

B. Index out of bounds when accessing arr[i+1]

C. Loop direction causes overwriting elements

D. No error, code works correctly

Solution

1. Step 1: Analyze loop direction and effect

   The loop moves forward from middle to end, copying arr[i] to arr[i+1], overwriting elements before they are moved.

2. Step 2: Identify correct approach

   Elements must be shifted right starting from the end backward to avoid overwriting data.

3. Final Answer:

   Loop direction causes overwriting elements -> Option C

4. Quick Check:

   Shift right must go backward to avoid overwrite [OK]

Hint: Shift elements right backward from end to middle [OK]

Common Mistakes:

• Shifting elements forward causing data loss
• Ignoring array bounds when shifting
• Assuming forward loop works for shifting right

5. Given an array arr = {5, 10, 15, 20, 25, 30} of size 6, after inserting element 99 at the middle index, what will be the final array?

hard

A. [5, 10, 15, 99, 20, 25, 30]

B. [5, 10, 99, 15, 20, 25, 30]

C. [5, 10, 15, 20, 99, 25, 30]

D. [5, 10, 15, 20, 25, 30, 99]

Solution

1. Step 1: Calculate middle index for even-sized array

   Array size n=6, middle index = n/2 = 3 (0-based indexing).

2. Step 2: Shift elements right from index 5 to 3

   Shift elements at indices 5,4,3 one position right to make space at index 3.

3. Step 3: Insert 99 at middle index

   Place 99 at index 3 after shifting.

4. Final Answer:

   [5, 10, 15, 99, 20, 25, 30] -> Option A

5. Quick Check:

   Insert at index 3 shifts right [OK]

Hint: For even size, middle = size/2; shift right, then insert [OK]

Common Mistakes:

• Inserting at index 2 instead of 3
• Not shifting elements before insertion
• Appending at the end instead of middle