Pointer and variable relationship in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pointer and variable modification

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

C++

#include <iostream>
int main() {
    int x = 10;
    int* p = &x;
    *p = 20;
    std::cout << x << std::endl;
    return 0;
}

A 20

B 10

C Compilation error

D Undefined behavior

💡 Hint

Remember that *p accesses the value pointed to by p.

The pointer p points to x. Changing *p changes x's value to 20. So printing x outputs 20.

❓ Predict Output

intermediate

Pointer reassignment effect

What is the output of this C++ code?

C++

#include <iostream>
int main() {
    int a = 5, b = 10;
    int* p = &a;
    p = &b;
    *p = 20;
    std::cout << a << " " << b << std::endl;
    return 0;
}

A 5 20

B 5 10

C 20 20

D 20 10

💡 Hint

Pointer p is changed to point to b before modifying *p.

Initially p points to a, but then p points to b. Changing *p changes b to 20. a remains 5.

❓ Predict Output

advanced

Pointer arithmetic and variable values

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

C++

#include <iostream>
int main() {
    int arr[3] = {1, 2, 3};
    int* p = arr;
    *(p + 1) = 10;
    std::cout << arr[1] << std::endl;
    return 0;
}

A 2

B 10

C Compilation error

D Undefined behavior

💡 Hint

Pointer arithmetic moves the pointer to the next element.

p points to arr[0]. *(p + 1) accesses arr[1], which is set to 10. So arr[1] prints 10.

❓ Predict Output

advanced

Pointer to pointer value change

What is the output of this C++ program?

C++

#include <iostream>
int main() {
    int x = 5;
    int* p = &x;
    int** pp = &p;
    **pp = 15;
    std::cout << x << std::endl;
    return 0;
}

A 5

B Compilation error

C 15

D Undefined behavior

💡 Hint

**pp accesses the value pointed to by the pointer p.

pp points to p, which points to x. Changing **pp changes x to 15.

❓ Predict Output

expert

Pointer and variable relationship with const correctness

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

C++

#include <iostream>
int main() {
    int x = 10;
    const int* p = &x;
    // *p = 20; // Uncommenting this line causes error
    x = 20;
    std::cout << *p << std::endl;
    return 0;
}

A Undefined behavior

B 10

C Compilation error

D 20

💡 Hint

const int* means you cannot change the value through the pointer, but the variable itself can change.

p points to x as a const pointer. Changing x directly to 20 updates the value. *p prints 20.