Memory allocation and deallocation in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of dynamic memory allocation with pointers

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

C++

#include <iostream>
int main() {
    int* p = new int(10);
    std::cout << *p << std::endl;
    delete p;
    return 0;
}

A 0

B Compilation error

C Runtime error

D 10

💡 Hint

Remember that new allocates memory and initializes the value.

The pointer p points to a dynamically allocated int initialized to 10. Dereferencing *p prints 10.

❓ Predict Output

intermediate

Output after deleting and accessing pointer

What happens when you run this C++ code?

C++

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

A Undefined behavior (may print garbage or crash)

B 5

C Compilation error

D 0

💡 Hint

Accessing memory after delete is unsafe.

After delete, the pointer p is dangling. Dereferencing it causes undefined behavior, which may print garbage or crash.

🧠 Conceptual

advanced

Correct use of delete[] for arrays

Which option correctly deallocates the dynamically allocated array in C++?

A int* arr = new int[5]; delete arr;

B int* arr = new int[5]; free(arr);

C int* arr = new int[5]; delete[] arr;

D int* arr = new int[5]; delete arr[0];

💡 Hint

Arrays allocated with new[] must be deallocated with delete[].

Using delete[] properly frees the entire array. Using delete without [] causes undefined behavior. free() is for malloc, not new.

❓ Predict Output

advanced

Output of double delete error

What error or output occurs when running this code?

C++

#include <iostream>
int main() {
    int* p = new int(7);
    delete p;
    delete p;
    std::cout << "Done" << std::endl;
    return 0;
}

A Runtime error (double free or corruption)

B 7

C Compilation error

D Done

💡 Hint

Deleting the same pointer twice causes a runtime error.

Double deleting a pointer causes undefined behavior, often a runtime error like double free or corruption.

🧠 Conceptual

expert

Memory leak detection in C++ code

Which option describes the memory leak in the following code snippet?

C++

void foo() {
    int* p = new int[10];
    p = new int[20];
    delete[] p;
}

A No memory leak; all allocated memory is freed.

B Memory leak because the first allocated array is lost without delete.

C Memory leak because delete[] is used incorrectly.

D Memory leak because p is deleted twice.

💡 Hint

Reassigning pointer without deleting old memory causes leak.

The first allocated array is overwritten by p = new int[20]; without deleting it first, causing a memory leak.