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

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of dynamic array allocation

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

C++

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

A 3

B 1

C 2

D Compilation error

💡 Hint

Remember that array indexing starts at 0.

The array is initialized with values {1, 2, 3}. arr[1] accesses the second element, which is 2.

❓ Predict Output

intermediate

Output of new operator with class object

What will this program print?

C++

#include <iostream>
class Box {
public:
    int length;
    Box(int l) : length(l) {}
};
int main() {
    Box* b = new Box(10);
    std::cout << b->length << std::endl;
    delete b;
    return 0;
}

A Runtime error

B 0

C Compilation error

D 10

💡 Hint

Check how the constructor initializes the length.

The Box object is created with length 10, so printing b->length outputs 10.

❓ Predict Output

advanced

Output when forgetting to delete dynamic memory

What is the output of this program?

C++

#include <iostream>
int main() {
    int* p = new int(5);
    *p = 10;
    std::cout << *p << std::endl;
    // no delete called
    return 0;
}

A 10

B 5

C Compilation error

D Runtime error due to memory leak

💡 Hint

The program prints the value pointed by p before exiting.

The pointer p points to an int initialized to 5, then changed to 10. The program prints 10. Not deleting causes a memory leak but no immediate runtime error.

❓ Predict Output

advanced

Output of new operator with placement new

What will this program output?

C++

#include <iostream>
#include <new>
int main() {
    char buffer[sizeof(int)];
    int* p = new(buffer) int(42);
    std::cout << *p << std::endl;
    p->~int();
    return 0;
}

A 0

B 42

C Compilation error

D Runtime error

💡 Hint

Placement new constructs an object in pre-allocated memory.

Placement new constructs an int with value 42 in buffer. Printing *p outputs 42.

🧠 Conceptual

expert

What error occurs when deleting non-dynamically allocated memory?

Consider this code snippet: int x = 5; int* p = &x; delete p; What happens when this code runs?

A Undefined behavior, likely runtime error

B Deletes x safely, no error

C Compilation error because delete cannot be used on stack variables

D Memory leak occurs

💡 Hint

delete should only be used on memory allocated with new.

Deleting a pointer to a stack variable causes undefined behavior and often runtime errors.