delete operator in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of deleting a dynamically allocated int

What is the output of this C++ code snippet?

C++

#include <iostream>
int main() {
    int* p = new int(10);
    std::cout << *p << std::endl;
    delete p;
    // std::cout << *p << std::endl; // Uncommenting this causes undefined behavior
    std::cout << "Deleted" << std::endl;
    return 0;
}

A

Runtime error

B

Deleted
10

C

10
Deleted

D

Compilation error

💡 Hint

Remember that deleting a pointer frees memory but does not print anything by itself.

The program prints the value pointed by p (10), then deletes the memory, and finally prints "Deleted". The delete operator does not produce output.

❓ Predict Output

intermediate

Effect of deleting an array allocated with new[]

What is the output of this C++ code?

C++

#include <iostream>
int main() {
    int* arr = new int[3]{1, 2, 3};
    delete arr;
    std::cout << arr[0] << std::endl;
    return 0;
}

A

Runtime error or undefined behavior

B

Compilation error

C

1

D

0

💡 Hint

Deleting an array allocated with new[] requires a special delete syntax.

Using delete instead of delete[] on an array causes undefined behavior. Accessing arr[0] after delete is also undefined.

❓ Predict Output

advanced

Output when deleting a nullptr pointer

What happens when you delete a nullptr pointer in C++?

C++

#include <iostream>
int main() {
    int* p = nullptr;
    delete p;
    std::cout << "Deleted nullptr" << std::endl;
    return 0;
}

A

Compilation error

B

Runtime error

C

No output

D

Deleted nullptr

💡 Hint

Deleting nullptr is safe and does nothing.

The delete operator does nothing when given a nullptr pointer. The program prints "Deleted nullptr".

❓ Predict Output

advanced

Output of deleting a pointer twice

What is the output or behavior of this code?

C++

#include <iostream>
int main() {
    int* p = new int(5);
    delete p;
    delete p;
    std::cout << "Done" << std::endl;
    return 0;
}

A

Runtime error (double free)

B

Done

C

Compilation error

D

Undefined output

💡 Hint

Deleting the same pointer twice causes a runtime error.

Double deleting a pointer causes undefined behavior and usually a runtime error like a crash.

🧠 Conceptual

expert

Which delete operator call is correct for this class?

Given the class below, which delete statement correctly frees the allocated memory without causing undefined behavior?

C++

class MyClass {
public:
    int* data;
    MyClass() { data = new int[5]; }
    ~MyClass() { delete[] data; }
};

int main() {
    MyClass* obj = new MyClass();
    // Which delete is correct here?
    // A) delete obj->data;
    // B) delete[] obj->data;
    // C) delete[] obj;
    // D) delete obj;
    return 0;
}

A delete[] obj->data;

B delete obj;

C delete[] obj;

D delete obj->data;

💡 Hint

Deleting the object calls its destructor which deletes the array properly.

The correct way is to delete the object pointer (delete obj;). This calls the destructor which deletes the array with delete[]. Deleting obj->data directly is unsafe here because the destructor also deletes it, causing double delete.