Array Insertion at End in DSA C++ - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output after inserting elements at the end of an array

What is the output of the following C++ code that inserts elements at the end of an array?

DSA C++

#include <iostream>
using namespace std;

int main() {
    int arr[5] = {1, 2, 3};
    int size = 3;
    int capacity = 5;

    if (size < capacity) {
        arr[size] = 4;
        size++;
    }
    if (size < capacity) {
        arr[size] = 5;
        size++;
    }

    for (int i = 0; i < size; i++) {
        cout << arr[i] << " ";
    }
    return 0;
}

A 1 2 3 4 5

B 1 2 3 4

C 1 2 3

D 1 2 3 5

💡 Hint

Check how many times the insertion condition is true and how size changes.

The code inserts 4 and then 5 at the end of the array because size is less than capacity twice. The final array printed is 1 2 3 4 5.

❓ Predict Output

intermediate

Resulting array after conditional insertion

What will be the output of this code snippet that tries to insert an element at the end only if there is space?

DSA C++

#include <iostream>
using namespace std;

int main() {
    int arr[4] = {10, 20, 30, 40};
    int size = 4;
    int capacity = 4;

    if (size < capacity) {
        arr[size] = 50;
        size++;
    }

    for (int i = 0; i < size; i++) {
        cout << arr[i] << " ";
    }
    return 0;
}

A Runtime error

B 10 20 30 40 50

C 10 20 30 40 0

D 10 20 30 40

💡 Hint

Check if the insertion condition is true or false.

Since size equals capacity, the insertion condition fails and no new element is added. The array remains unchanged.

🔧 Debug

advanced

Identify the error in array insertion code

What error will this code produce when trying to insert an element at the end of the array?

DSA C++

#include <iostream>
using namespace std;

int main() {
    int arr[3] = {5, 10, 15};
    int size = 3;
    int capacity = 3;

    arr[size] = 20;
    size++;

    for (int i = 0; i < size; i++) {
        cout << arr[i] << " ";
    }
    return 0;
}

A Runtime error: Array index out of bounds

B Compilation error

C 5 10 15 20

D 20 10 15 20

💡 Hint

Check if the code respects the array capacity before insertion.

The code writes to arr[3] which is outside the declared array size of 3, causing undefined behavior or runtime error.

🧠 Conceptual

advanced

Understanding array insertion at end with fixed size

Why is it important to check the array capacity before inserting an element at the end?

A To avoid overwriting existing elements and causing data loss

B To ensure the array elements remain sorted after insertion

C To prevent accessing memory outside the array bounds which can cause crashes or bugs

D To reduce the time complexity of insertion operation

💡 Hint

Think about what happens if you write beyond the array size in memory.

Accessing or writing outside the array bounds can cause crashes, unpredictable behavior, or security issues.

🚀 Application

expert

Predict the final array after multiple insertions with capacity check

Given the following code, what is the final printed array?

DSA C++

#include <iostream>
using namespace std;

int main() {
    int arr[6] = {2, 4, 6};
    int size = 3;
    int capacity = 6;

    int to_insert[] = {8, 10, 12, 14};
    int n = 4;

    for (int i = 0; i < n; i++) {
        if (size < capacity) {
            arr[size] = to_insert[i];
            size++;
        }
    }

    for (int i = 0; i < size; i++) {
        cout << arr[i] << " ";
    }
    return 0;
}

A 2 4 6 8 10 12 14 0

B 2 4 6 8 10 12

C 2 4 6 8 10 12 14

D 2 4 6 8 10 12 14 14

💡 Hint

Check how many elements can fit given the capacity and initial size.

The array capacity is 6, initial size 3, so only 3 elements from to_insert can be added. The last element 14 is not inserted.

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