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 an array. Sometimes, a new temperature reading arrives that needs to be inserted exactly in the middle of the current list to keep the order balanced.

🎯 Goal: Build a program that inserts a new temperature value into the middle of an existing array and then prints the updated array.

📋 What You'll Learn

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

Create an integer variable called new_temp and set it to 27

Write code to insert new_temp into the middle index of temps, shifting elements to the right

Print the updated array elements separated by spaces

💡 Why This Matters

🌍 Real World

In real life, inserting data into the middle of a list is common when managing ordered records like temperature logs, event schedules, or priority queues.

💼 Career

Understanding how to manipulate arrays and insert elements is a fundamental skill 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 temps with these exact values: 23, 25, 22, 24, 26

DSA C

# Create the array temps with 5 values
// Your code here

Hint

Use int temps[6] = {23, 25, 22, 24, 26}; to create the array with space for one extra element.

2

Add the new temperature variable

Create an integer variable called new_temp and set it to 27

DSA C

#include 

int main() {
    int temps[6] = {23, 25, 22, 24, 26};
    // Create new_temp variable
    // Your code here
    return 0;
}

Hint

Declare int new_temp = 27; inside main().

3

Insert the new temperature at the middle index

Write code to insert new_temp into the middle index 2 of temps, shifting elements from index 2 to the right

DSA C

#include 

int main() {
    int temps[6] = {23, 25, 22, 24, 26};
    int new_temp = 27;
    // Insert new_temp at index 2
    // Your code here
    return 0;
}

Hint

Shift elements from the end to index 3 to make space at index 2, then assign new_temp to temps[2].

4

Print the updated array

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

DSA C

#include 

int main() {
    int temps[6] = {23, 25, 22, 24, 26};
    int new_temp = 27;
    for (int i = 5; i > 2; i--) {
        temps[i] = temps[i - 1];
    }
    temps[2] = new_temp;
    // Print the updated array
    // Your code here
    return 0;
}

Hint

Use printf inside a loop to print each element with a space, then print a newline.

Practice

1. What is the correct middle index to insert an element in an array of size 6?

easy

A. 5

B. 2

C. 4

D. 3

Solution

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

   For an array of size 6, middle index is size/2 = 6/2 = 3.

2. Step 2: Confirm insertion position

   Inserting at index 3 places the element exactly in the middle.

3. Final Answer:

   3 -> Option D

4. Quick Check:

   Middle index = size/2 = 3 [OK]

Hint: Middle index = array size divided by 2 [OK]

Common Mistakes:

• Using size-1 as middle index
• Using size/2 - 1 for even size
• Confusing zero-based indexing

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

easy

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

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

C. int mid = n / 2; arr[mid] = x;

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

Solution

1. Step 1: Identify correct shifting direction

   To insert at middle, elements from middle to end must shift right to make space.

2. Step 2: Check code correctness

   int mid = n / 2; for(int i = n; i > mid; i--) arr[i] = arr[i-1]; arr[mid] = x; shifts elements right from end to middle, then inserts x at mid. Others shift incorrectly or overwrite.

3. Final Answer:

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

4. Quick Check:

   Shift right from end to mid, then insert [OK]

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

Common Mistakes:

• Shifting elements left instead of right
• Not shifting elements before insertion
• Overwriting elements without shifting

3. What will be the content of the 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 is 5, middle index = 5/2 = 2 (integer division).

2. Step 2: Shift elements right and insert 99

   Shift elements from index 4 to 2 right by one position. Insert 99 at index 2.

3. Final Answer:

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

4. Quick Check:

   Insert at index 2 shifts elements right [OK]

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

Common Mistakes:

• Inserting at wrong index
• Not shifting elements before insertion
• Overwriting elements

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

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

medium

A. Loop should run backwards from n to mid

B. Index mid is incorrect for insertion

C. No need to shift elements before insertion

D. Array size n should be incremented before insertion

Solution

1. Step 1: Analyze loop direction

   The loop shifts elements from mid to n forward, but does so from low to high index, causing overwrite.

2. Step 2: Correct loop direction

   Loop must run backwards from n to mid to shift elements right safely without overwriting.

3. Final Answer:

   Loop should run backwards from n to mid -> Option A

4. Quick Check:

   Shift right must be done backwards [OK]

Hint: Shift elements right by looping backwards from end [OK]

Common Mistakes:

• Looping forward causing data overwrite
• Not updating array size after insertion
• Incorrect middle index calculation

5. Given an array arr = {5, 10, 15, 20, 25, 30} of size 6, write the final array after inserting 99 at the middle index and then inserting 77 at the new middle index of the updated array.

hard

A. [5, 10, 15, 77, 99, 20, 25, 30]

B. [5, 10, 77, 99, 15, 20, 25, 30]

C. [5, 10, 99, 15, 77, 20, 25, 30]

D. [5, 10, 15, 99, 77, 20, 25, 30]

Solution

1. Step 1: Insert 99 at middle of original array

   Original size = 6, middle index = 3. Insert 99 at index 3 shifting elements right: [5, 10, 15, 99, 20, 25, 30]

2. Step 2: Insert 77 at middle of updated array

   New size = 7, middle index = 7/2 = 3. Insert 77 at index 3 shifting elements right: [5, 10, 15, 77, 99, 20, 25, 30]

3. Final Answer:

   [5, 10, 15, 77, 99, 20, 25, 30] -> Option A

4. Quick Check:

   Insert twice at middle recalculating index each time [OK]

Hint: Recalculate middle after each insertion before next insert [OK]

Common Mistakes:

• Not recalculating middle index after first insertion
• Overwriting elements without shifting
• Inserting at wrong index second time