Why pointers are needed in C++ - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pointer manipulation

What is the output of this C++ code that uses pointers to change a variable's value?

C++

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

A 10

B 20

C Compilation error

D Runtime error

💡 Hint

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

The pointer p holds the address of x. Using *p = 20 changes the value of x to 20. So printing x outputs 20.

🧠 Conceptual

intermediate

Why use pointers for function arguments?

Why do we use pointers as function arguments in C++?

A To allow the function to modify the original variable's value

B To make the function run faster by avoiding copying variables

C To prevent the function from accessing the variable

D To make the variable constant inside the function

💡 Hint

Think about what happens when you want a function to change a variable outside its own scope.

Passing a pointer lets the function access and change the original variable's value, not just a copy.

❓ Predict Output

advanced

Output of pointer arithmetic

What is the output of this C++ code that uses pointer arithmetic on an array?

C++

#include <iostream>
int main() {
    int arr[] = {5, 10, 15};
    int* p = arr;
    std::cout << *(p + 1) << std::endl;
    return 0;
}

A 5

B Compilation error

C 10

D 15

💡 Hint

Pointer arithmetic moves the pointer to the next element in the array.

p points to arr[0]. Adding 1 moves it to arr[1], which is 10.

🔧 Debug

advanced

Identify the pointer error

What error will this C++ code produce?

C++

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

A Compilation error: uninitialized pointer

B No error, outputs garbage value

C Output: 10

D Runtime error: segmentation fault

💡 Hint

Think about what happens if you dereference a pointer that does not point to valid memory.

The pointer p is uninitialized and points to an unknown location. Dereferencing it causes a runtime crash (segmentation fault).

🚀 Application

expert

Using pointers to swap two variables

Which option correctly swaps the values of two integers using pointers in C++?

C++

void swap(int* a, int* b) {
    // Fill in
}

int main() {
    int x = 3, y = 7;
    swap(&x, &y);
    std::cout << x << " " << y << std::endl;
    return 0;
}

A int temp = *a; *a = *b; *b = temp;

B int temp = a; a = b; b = temp;

C *a = *b; *b = *a;

D int temp = *a; *b = *a; *a = temp;

💡 Hint

Remember to use * to access the values the pointers point to, and swap them using a temporary variable.

Option A correctly uses a temporary variable to swap the values pointed to by a and b. Other options either swap pointers or overwrite values incorrectly.