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

Array Insertion at End

📖 Scenario: You are managing a list of daily temperatures recorded in a small weather station. Each day, a new temperature reading is added to the end of the list.

🎯 Goal: Build a simple program that stores temperature readings in an array and adds a new temperature at the end.

📋 What You'll Learn

Create an integer array called temperatures with the values 23, 25, 22, 20, 24

Create an integer variable called size that holds the current number of elements in temperatures

Create an integer variable called new_temp and set it to 26

Add new_temp to the end of the temperatures array by updating the array and size

Print the updated temperatures array elements separated by spaces

💡 Why This Matters

🌍 Real World

Adding new data points to a list is common in many applications like weather tracking, sales records, or sensor data collection.

💼 Career

Understanding how to manage arrays and insert data is fundamental for programming jobs that involve data processing and storage.

1

Create the initial array

Create an integer array called temperatures with the values 23, 25, 22, 20, 24.

DSA C++

# Create the integer array temperatures with values 23, 25, 22, 20, 24
# Your code here

Hint

Use int temperatures[10] = {23, 25, 22, 20, 24}; to create the array with extra space for new elements.

2

Set the current size and new temperature

Create an integer variable called size and set it to 5. Then create an integer variable called new_temp and set it to 26.

DSA C++

int temperatures[10] = {23, 25, 22, 20, 24};
# Create size = 5 and new_temp = 26
# Your code here

Hint

Use int size = 5; and int new_temp = 26; to set the current count and new value.

3

Insert the new temperature at the end

Add new_temp to the end of the temperatures array by assigning it to temperatures[size]. Then increase size by 1.

DSA C++

int temperatures[10] = {23, 25, 22, 20, 24};
int size = 5;
int new_temp = 26;
# Insert new_temp at the end and update size
# Your code here

Hint

Assign temperatures[size] = new_temp; and then increase size by 1 with size++;.

4

Print the updated array

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

DSA C++

int temperatures[10] = {23, 25, 22, 20, 24};
int size = 5;
int new_temp = 26;
temperatures[size] = new_temp;
size++;
# Print all elements of temperatures separated by spaces
# Your code here

Hint

Use a for loop to print each element followed by a space. End with cout << endl;.

Practice

1. What happens when you insert an element at the end of a fixed-size array in C++ without resizing?

easy

A. The element replaces the last element if the array is full

B. The array automatically resizes to fit the new element

C. The element is added at the next free position if available

D. The program throws a runtime error

Solution

1. Step 1: Understand fixed-size array behavior

   Fixed-size arrays have a set size and cannot grow automatically.

2. Step 2: Inserting at end when full

   If the array is full, you cannot add a new element without overwriting or causing undefined behavior. If there is space available, the element is added at the next free position.

3. Final Answer:

   The element is added at the next free position if available -> Option C

4. Quick Check:

   Fixed-size array adds element only if space available [OK]

Hint: Fixed arrays don't resize; add element only if space available [OK]

Common Mistakes:

• Assuming array resizes automatically
• Thinking insertion always adds new space
• Expecting runtime error on insertion

2. Which of the following is the correct syntax to insert an element `x` at the end of a vector `v` in C++?

easy

A. v.append(x);

B. v.push_back(x);

C. v.add(x);

D. v.insert_end(x);

Solution

1. Step 1: Recall vector insertion method

   The standard method to add an element at the end of a vector is push_back.

2. Step 2: Check syntax correctness

   Only v.push_back(x); is valid C++ syntax for vector insertion at end.

3. Final Answer:

   v.push_back(x); -> Option B

4. Quick Check:

   Use push_back to insert at vector end [OK]

Hint: Use push_back() to add at vector end [OK]

Common Mistakes:

• Using non-existent methods like insert_end or add
• Confusing vector with other container methods
• Using append which is not a C++ vector method

3. What will be the output of the following C++ code?

int arr[5] = {1, 2, 3, 4, 5};
int n = 5;
int x = 10;
if (n < 5) {
  arr[n] = x;
  n++;
}
for (int i = 0; i < n; i++) {
  std::cout << arr[i] << " ";
}

medium

A. 1 2 3 4 10

B. 1 2 3 4 5 10

C. Compilation error

D. 1 2 3 4 5

Solution

1. Step 1: Check condition for insertion

   The condition if (n < 5) is false because n equals 5, so insertion does not happen.

2. Step 2: Print array elements

   The loop prints all elements from index 0 to 4, which are 1 2 3 4 5.

3. Final Answer:

   1 2 3 4 5 -> Option D

4. Quick Check:

   Insertion skipped, original array printed [OK]

Hint: Check insertion condition before adding element [OK]

Common Mistakes:

• Assuming insertion happens even if condition false
• Printing beyond array size
• Confusing array size with variable n

4. Identify the error in the following code that tries to insert an element at the end of an array:

int arr[3] = {1, 2, 3};
int n = 3;
int x = 4;
arr[n] = x;
n++;
for (int i = 0; i < n; i++) {
  std::cout << arr[i] << " ";
}

medium

A. Array index out of bounds when inserting element

B. Variable n is not incremented correctly

C. Missing semicolon after arr[n] = x

D. Loop condition should be i <= n

Solution

1. Step 1: Check array size and insertion index

   Array size is 3, valid indices are 0,1,2. Inserting at arr[3] is out of bounds.

2. Step 2: Understand consequences of out-of-bounds access

   Accessing arr[3] causes undefined behavior or runtime error.

3. Final Answer:

   Array index out of bounds when inserting element -> Option A

4. Quick Check:

   Insertion index must be within array size [OK]

Hint: Array indices go from 0 to size-1 only [OK]

Common Mistakes:

• Ignoring array bounds when inserting
• Assuming array resizes automatically
• Incorrect loop boundary causing extra prints

5. You have an array `int arr[6] = {1, 2, 3, 4, 5};` and a variable `int n = 5;` representing the current number of elements. Write the correct code snippet to insert `10` at the end safely, considering array size limits.

hard

A. if (n < 6) { arr[n] = 10; n++; }

B. arr[n] = 10; n++;

C. if (n <= 6) { arr[n] = 10; n++; }

D. if (n < 5) { arr[n] = 10; n++; }

Solution

1. Step 1: Check array capacity before insertion

   Array size is 6, so insertion is safe only if n < 6.

2. Step 2: Insert element and update count

   If condition is true, assign arr[n] = 10 and increment n to reflect new size.

3. Final Answer:

   if (n < 6) { arr[n] = 10; n++; } -> Option A

4. Quick Check:

   Check capacity before insert, then add element [OK]

Hint: Always check n < array size before inserting [OK]

Common Mistakes:

• Not checking array size before insertion
• Using <= instead of < causing overflow
• Wrong size limit in condition