Summary - Pointer basics

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.

Exercise 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.

Show example 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;
}

Exercise 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.

Show example 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;
}

Test yourself

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
Error

Show answer

9 5 — swap(&x, &y) exchanges the values of x and y.

swap call
```
swap(____, &y);
```
Show answer
```
swap(&x, &y);
```
Match the pointer tools

int* p

Pointer declaration
&x

Take address
*p

Access value
p + 1

Next element

Next lesson: Task model

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