Reference vs pointer in C++ - Practice Questions

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of reference and pointer modification

What is the output of this C++ code?

C++

#include <iostream>

int main() {
    int x = 10;
    int &ref = x;
    int *ptr = &x;
    ref = 20;
    *ptr = 30;
    std::cout << x << std::endl;
    return 0;
}

A 10

B 20

C Compilation error

D 30

💡 Hint

Remember that both reference and pointer can modify the original variable.

Both the reference and the pointer refer to the same variable x. First, ref = 20 changes x to 20, then *ptr = 30 changes x to 30. So the final output is 30.

❓ Predict Output

intermediate

Pointer vs reference reassignment

What is the output of this C++ code?

C++

#include <iostream>

int main() {
    int a = 5, b = 10;
    int *ptr = &a;
    int &ref = a;
    ptr = &b;
    ref = b;
    std::cout << a << " " << b << std::endl;
    return 0;
}

A 10 10

B 5 5

C 5 10

D Compilation error

💡 Hint

Remember that references cannot be reseated but pointers can.

The pointer ptr is changed to point to b, but the reference ref still refers to a. However, ref = b assigns the value of b to a, so a becomes 10. b remains 10. So output is '10 10'.

🔧 Debug

advanced

Identify the error in pointer and reference usage

Which option will cause a compilation error in this code snippet?

C++

int x = 5;
int &ref = x;
int *ptr = &x;

// Options below show different assignments:

A ptr = &ref;

B int &newRef = ptr;

C ref = 10;

D *ptr = 20;

💡 Hint

Check if the types on both sides match for references.

Option B tries to create a reference to an int pointer (int*), but declares it as int& which is a reference to int. This is a type mismatch causing a compilation error.

🧠 Conceptual

advanced

Difference in memory behavior of references and pointers

Which statement correctly describes the difference between references and pointers in C++?

A Pointers can be reseated to point to different objects, references cannot be reseated after initialization.

B References require explicit dereferencing to access the value, pointers do not.

C References can be null, pointers cannot.

D Pointers are automatically dereferenced when used, references require the * operator.

💡 Hint

Think about whether you can change what a reference or pointer points to after creation.

Pointers can be changed to point to different objects anytime. References must be initialized once and cannot be changed to refer to another object later.

❓ Predict Output

expert

Output of complex pointer and reference manipulation

What is the output of this C++ code?

C++

#include <iostream>

void func(int *&ptrRef, int &ref) {
    *ptrRef = ref + 5;
    ref = *ptrRef + 5;
    ptrRef = &ref;
}

int main() {
    int a = 1, b = 2;
    int *p = &a;
    func(p, b);
    std::cout << a << " " << b << " " << *p << std::endl;
    return 0;
}

A 1 2 1

B 7 7 7

C 7 12 12

D Compilation error

💡 Hint

Track carefully how the pointer reference and reference parameters modify values and pointers.

Initially, p points to a=1, b=2. *ptrRef = ref + 5; sets *p = 2 + 5 = 7, so a=7. ref = *ptrRef + 5; sets b = 7 + 5 = 12. ptrRef = &ref; now p points to b. In main, a=7, b=12, *p = b = 12. Output: '7 12 12'.