Pointers in C

A pointer is a variable that stores the memory address of another variable.

Every variable lives somewhere in RAM. A pointer tells us where that place is.

Two key terms:

• & → address of operator
• * → value at address (dereference)

The * is used while declaring a pointer variable.

#include 

int main() {

    int a = 10;
    int *p = &a; // pointer storing address of a

    printf("Value of a = %d\n", a);
    printf("Address of a = %p\n", &a);
    printf("Pointer p stores = %p\n", p);
    printf("Value at pointer p = %d\n", *p);

    return 0;
}

Dereferencing means accessing the value stored at the pointer’s address.

#include 

int main() {

    int x = 25;
    int *ptr = &x;

    printf("x = %d\n", x);
    printf("*ptr = %d\n", *ptr); // same value as x

    return 0;
}

You can modify a variable through a pointer.

#include 

int main() {

    int n = 5;
    int *p = &n;

    *p = 100; // changes n

    printf("n = %d\n", n);

    return 0;
}

Pointers can move between memory locations. When you add 1 to an int*, it moves by 4 bytes.

#include 

int main() {

    int arr[3] = {10, 20, 30};
    int *p = arr; // points to arr[0]

    printf("%d\n", *p);     // 10
    printf("%d\n", *(p+1)); // 20
    printf("%d\n", *(p+2)); // 30

    return 0;
}

Functions normally get a copy of variables. Pointers allow the function to modify the original value.

#include 

void change(int *x) {
    *x = 200;
}

int main() {

    int n = 10;
    change(&n);

    printf("n = %d\n", n);

    return 0;
}