Summary - Pointer basics
- C++ course
- Beginner
- Lesson 82/116
- 5 min
Combine &, * and nullptr to write a swap function.
Summary - Pointer basics
In this group you learned the core tools of pointers: declaring, taking an address with &, accessing a value with *, the empty state with nullptr, and pointer arithmetic. Pointers unlock the low-level power of C++.
There are two tasks. First, you will write a swap function with two pointer parameters. Second, you will sum the elements of an array using pointer arithmetic. Both combine what you have learned.
Practice The swap(int*, int*) function
Define a void swap(int* a, int* b) function; in the body exchange *a and *b using an int t temporary variable. In main declare int x = 5, y = 9;, call swap(&x, &y), and print x and y on the same line separated by a space.
Starter code
#include <iostream>
// Define the swap function
int main() {
// Declare x and y
// Add a swap call
// Print x and y
return 0;
}Sample solution
#include <iostream>
void swap(int* a, int* b) {
int t = *a;
*a = *b;
*b = t;
}
int main() {
int x = 5, y = 9;
swap(&x, &y);
std::cout << x << " " << y << "\n";
return 0;
}Expected output
9 5
Practice Array sum with a pointer
Declare int arr[] = {2, 4, 6};. Start with int* p = arr;. Write int sum = *p + *(p + 1) + *(p + 2); to sum the three elements. Print sum with std::cout.
Starter code
#include <iostream>
int main() {
// Declare the array
// Bind p to the array
// Sum with pointer arithmetic
// Print the sum
return 0;
}Sample solution
#include <iostream>
int main() {
int arr[] = {2, 4, 6};
int* p = arr;
int sum = *p + *(p + 1) + *(p + 2);
std::cout << sum << "\n";
return 0;
}Expected output
12
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does this code print?
void swap(int* a, int* b) {
int t = *a;
*a = *b;
*b = t;
}
int main() {
int x = 5, y = 9;
swap(&x, &y);
std::cout << x << " " << y;
return 0;
}- 5 9
- 5 5
- 9 5 Correct answer
- Error
Explanation: swap(&x, &y) exchanges the values of x and y.
2 swap call
swap(____, &y);swap(&x, &y);Explanation: swap(&x, &y) passes the addresses of x and y.
3 Match the pointer tools
| Term | Meaning |
|---|---|
int* p |
Pointer declaration |
&x |
Take address |
*p |
Access value |
p + 1 |
Next element |