Array Insertion at Middle Index in DSA C - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output after inserting element in the middle of an array

What is the output of the following C code after inserting the value 99 at the middle index of the array?

DSA C

int main() {
    int arr[6] = {10, 20, 30, 40, 50};
    int n = 5;
    int val = 99;
    int mid = n / 2;
    for (int i = n; i > mid; i--) {
        arr[i] = arr[i - 1];
    }
    arr[mid] = val;
    n++;
    for (int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    return 0;
}

A 10 20 30 40 99 50

B 10 20 30 99 40 50

C 10 20 99 30 40 50

D 10 20 30 40 50 99

💡 Hint

Remember that integer division truncates, so middle index is n/2 = 2 for n=5.

The middle index for an array of size 5 is 2 (0-based). The code shifts elements from the end to the middle index to the right by one position, then inserts 99 at index 2. The resulting array is: 10 20 99 30 40 50.

🧠 Conceptual

intermediate

Understanding middle index calculation for array insertion

Given an array of length n, which formula correctly calculates the middle index to insert a new element so that the array remains balanced?

A middle = (n + 1) / 2

B middle = (n - 1) / 2

C middle = n - 1

D middle = n / 2

💡 Hint

Consider zero-based indexing and integer division truncation.

For zero-based arrays, the middle index is calculated as n / 2 using integer division. This places the new element roughly in the center, balancing elements on both sides.

🔧 Debug

advanced

Identify the error in array insertion code

What error will occur when running this code snippet that inserts an element at the middle of an array of size 5? int arr[5] = {1, 2, 3, 4, 5}; int n = 5; int val = 10; int mid = n / 2; for (int i = n; i > mid; i--) { arr[i] = arr[i - 1]; } arr[mid] = val; n++;

A Buffer overflow (writing outside array bounds)

B No error, runs correctly

C Segmentation fault due to null pointer

D Compilation error due to syntax

💡 Hint

Check the array size and the index used in the loop.

The array size is 5, but the loop writes to arr[5], which is outside the allocated memory, causing buffer overflow.

❓ Predict Output

advanced

Output after multiple insertions at middle index

What is the output after inserting values 99 and then 77 at the middle index of the array?

DSA C

int main() {
    int arr[8] = {1, 2, 3, 4, 5, 6};
    int n = 6;
    int val1 = 99;
    int val2 = 77;
    int mid = n / 2;
    // Insert 99
    for (int i = n; i > mid; i--) {
        arr[i] = arr[i - 1];
    }
    arr[mid] = val1;
    n++;
    // Insert 77
    mid = n / 2;
    for (int i = n; i > mid; i--) {
        arr[i] = arr[i - 1];
    }
    arr[mid] = val2;
    n++;
    for (int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    return 0;
}

A 1 2 3 77 99 4 5 6

B 1 2 3 99 77 4 5 6

C 1 2 3 99 4 77 5 6

D 1 2 3 4 77 99 5 6

💡 Hint

Remember to recalculate middle index after first insertion.

After first insertion, array is: 1 2 3 99 4 5 6 New size n=7, middle index = 7/2=3 Second insertion shifts elements from index 3, inserts 77 at index 3. Final array: 1 2 3 77 99 4 5 6

🧠 Conceptual

expert

Time complexity of inserting an element at the middle of an array

What is the time complexity of inserting an element at the middle index of an array of size n, assuming shifting elements is required?

A O(1)

B O(n)

C O(log n)

D O(n^2)

💡 Hint

Consider how many elements need to be moved to make space.

Inserting at the middle requires shifting about half the elements, which is proportional to n, so time complexity is O(n).