What are Pointers?

Pointers are a way or referencing a memory address. They allow you to directly manipulate memory locations and are essential for low-level programming tasks.

Different languages have different ways of using pointers but for this demonstration I will use C.

Regular Variables

When declaring a variable you would do this:

// <data-type> <name> = <value>;
int num = 10;

What this does it takes up an address in memory and sets the value to the value you set. You can then access it by using the variable directly:

printf("%d", num);
// 10

If you were to look at the memory table somewhere in there would be an entry with a value 10. It would look something like this:

If you were to update the variable, the value in the same memory address would also be updated.

num = 20;

Pointer Variables

To create a pointer in C you would use the * and & characters (known as asterisk and ampersand).

int num = 10;
int *num_pointer = #

In this example we have declare a variable called num with a value of 10. We have also declared a pointer variable called num_pointer with a value of the address of variable num. There's 2 parts to break down here, the asterisk and the ampersand. Firstly the * tells the compiler that this variable is a pointer variable so it can be used to manipulate memory locations. The & tells the compiler to get the address of the variable that comes after it. So the memory address table would look something like this:

If you want to get the value of what the pointer is pointing towards you would use the * again:

printf("%d", *num_pointer);
// 10

If we want to change the value of variable num we can now do so two different ways; by using the num variable as usual or by using the pointer variable. Both ways will change the same underlying value.

int num = 10;
int *num_pointer = #

printf("%d, %d", num, *num_pointer);
// 10, 10

num = 20;
printf("%d, %d", num, *num_pointer);
// 20, 20

*num_pointer = 30;
printf("%d, %d", num, *num_pointer);
// 30, 30

Resources

YouTube video by @Low Level