Array Insertion at Beginning in DSA C++ - Build from Scratch

Array Insertion at Beginning

📖 Scenario: You are managing a list of daily tasks. You want to add a new urgent task at the start of your list so it gets done first.

🎯 Goal: Learn how to insert an element at the beginning of an array by shifting existing elements to the right.

📋 What You'll Learn

Create an integer array with 5 specific tasks represented by numbers

Create a variable to hold the new urgent task value

Write code to insert the new task at the beginning by shifting existing elements

Print the updated array after insertion

💡 Why This Matters

🌍 Real World

In task management apps, urgent tasks often need to be added at the start of the list to prioritize them.

💼 Career

Understanding array manipulation is fundamental for software development, especially in systems programming and performance-critical applications.

1

Create the initial array

Create an integer array called tasks with these exact values: 10, 20, 30, 40, 50

DSA C++

# Create the array tasks with values 10, 20, 30, 40, 50
// Your code here

Hint

Use int tasks[6] = {10, 20, 30, 40, 50}; to create the array with space for 6 elements.

2

Create the new task variable

Create an integer variable called newTask and set it to 5

DSA C++

int tasks[6] = {10, 20, 30, 40, 50};
// Create newTask variable and set it to 5
// Your code here

Hint

Use int newTask = 5; to create the new task variable.

3

Insert the new task at the beginning

Use a for loop with variable i starting from 4 down to 0 to shift elements in tasks one position to the right, then set tasks[0] to newTask

DSA C++

int tasks[6] = {10, 20, 30, 40, 50};
int newTask = 5;
// Shift elements right and insert newTask at tasks[0]
// Your code here

Hint

Start the loop at index 4 and move each element one step right. Then place newTask at index 0.

4

Print the updated array

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

DSA C++

int tasks[6] = {10, 20, 30, 40, 50};
int newTask = 5;
for (int i = 4; i >= 0; i--) {
    tasks[i + 1] = tasks[i];
}
tasks[0] = newTask;
// Print all elements of tasks separated by spaces
// Your code here

Hint

Use a loop from 0 to 5 and print each element with a space after it.

Practice

1. What happens when you insert an element at the beginning of an array in C++?

easy

A. All existing elements shift one position to the right to make space.

B. The new element replaces the first element without shifting others.

C. The array size decreases by one.

D. The array elements are sorted automatically.

Solution

1. Step 1: Understand array structure

   An array stores elements in continuous memory locations.

2. Step 2: Effect of insertion at beginning

   To insert at the start, all elements must move right to free the first position.

3. Final Answer:

   All existing elements shift one position to the right to make space. -> Option A

4. Quick Check:

   Insertion at start shifts elements right = B [OK]

Hint: Insertion at start shifts elements right to free first slot [OK]

Common Mistakes:

• Thinking new element replaces first without shifting
• Assuming array size decreases
• Believing array sorts automatically

2. Which of the following is the correct syntax to insert an element `x` at the beginning of an array `arr` of size `n` in C++ (assuming enough space)?

easy

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

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

C. for(int i = n; i > 0; i--) arr[i] = arr[i-1]; arr[0] = x; n++;

D. arr[n] = x; n++;

Solution

1. Step 1: Shift elements right from end

   Loop from last index `n` down to 1, moving each element to the right by one.

2. Step 2: Insert new element at index 0 and increase size

   Place `x` at `arr[0]` and increment `n`.

3. Final Answer:

   for(int i = n; i > 0; i--) arr[i] = arr[i-1]; arr[0] = x; n++; -> Option C

4. Quick Check:

   Shift right from end, insert at 0 = C [OK]

Hint: Shift from end to start, then insert at zero index [OK]

Common Mistakes:

• Shifting from start to end overwrites data
• Not incrementing array size
• Inserting without shifting elements

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

int arr[5] = {2, 4, 6, 8, 10};
int n = 5;
int x = 1;
for(int i = n; i > 0; i--) {
  arr[i] = arr[i-1];
}
arr[0] = x;
n++;
for(int i = 0; i < n; i++) {
  std::cout << arr[i] << " ";
}

medium

A. 2 4 6 8 10 1

B. 1 2 4 6 8 10

C. 1 2 4 6 8

D. 2 4 6 8 10

Solution

1. Step 1: Shift elements right to make space

   Elements move right: arr[5]=arr[4]=10, arr[4]=arr[3]=8, arr[3]=arr[2]=6, arr[2]=arr[1]=4, arr[1]=arr[0]=2.

2. Step 2: Insert 1 at arr[0] and print

   arr[0]=1, array becomes [1,2,4,6,8,10], printed with space.

3. Final Answer:

   1 2 4 6 8 10 -> Option B

4. Quick Check:

   Shift right + insert 1 at start = A [OK]

Hint: Shift right, insert new at zero, print all elements [OK]

Common Mistakes:

• Not shifting elements correctly
• Printing old array size
• Inserting at wrong index

4. Identify the error in this code snippet that inserts `x` at the beginning of array `arr` of size `n`:

for(int i = 0; i < n; i++) {
  arr[i+1] = arr[i];
}
arr[0] = x;
n++;

medium

A. Loop shifts elements left instead of right, overwriting data.

B. Array size `n` is not incremented after insertion.

C. New element is inserted at wrong index.

D. Loop should start from `n` and go down to 1 to avoid overwrite.

Solution

1. Step 1: Analyze loop direction

   Loop moves from 0 to n-1, shifting elements forward, overwriting original data.

2. Step 2: Correct loop direction

   Loop must run backward from n to 1 to shift elements safely without overwrite.

3. Final Answer:

   Loop should start from `n` and go down to 1 to avoid overwrite. -> Option D

4. Quick Check:

   Backward loop prevents overwrite = D [OK]

Hint: Shift elements backward from end to start to avoid overwrite [OK]

Common Mistakes:

• Shifting elements forward overwrites data
• Forgetting to increment array size
• Inserting element at wrong position

5. Given an array `arr` of size `n` with elements sorted in ascending order, how can you insert a new element `x` at the beginning and keep the array sorted?

hard

A. If `x` is smaller than `arr[0]`, shift elements right and insert `x` at start; else find correct position.

B. Insert `x` at the beginning and then sort the entire array again.

C. Always insert `x` at the beginning without shifting elements.

D. Replace the last element with `x` if `x` is smaller than last element.

Solution

1. Step 1: Check if `x` is smaller than first element

   If yes, shift all elements right and insert `x` at index 0 to keep order.

2. Step 2: If `x` is not smallest, find correct position

   Find proper index to insert `x` to maintain sorted order, not necessarily at start.

3. Final Answer:

   If `x` is smaller than `arr[0]`, shift elements right and insert `x` at start; else find correct position. -> Option A

4. Quick Check:

   Insert at start only if smaller, else find position = A [OK]

Hint: Insert at start only if smaller; else find correct sorted position [OK]

Common Mistakes:

• Always inserting at start breaks sorting
• Sorting entire array after insertion wastes time
• Replacing last element loses data