Hands-on C: Understanding Pointers step by step

Quick Intro

Pointers have always been the most confusing aspect of C for new learners.

As a former lecturer, I find simple hands-on examples are the best to get one started.

In this article, I will explain the following:

• What a pointer is
• How a pointer is declared in C
• How to assign a memory address to a pointer
• How to change values using pointers
• How to move pointer to a different memory address

What is a pointer?

It's literally a variable that stores and point to the memory address of another variable.

Don't worry, it should be clear once we go through some examples.

How a pointer is declared in C

How to assign a memory address to a pointer

Now, imagine there's a variable x like this:

The &x just means we're assigning to p the memory address of x:

In order to retrieve the value 5 from p, we also need to use *p because p (without *) retrieves the memory address of x and *p goes after the value stored in the memory's address.

Here's the proof:

Notice that C understands that adding & in front of variable retrieves its memory address.

How to retrieve pointer's value

Retrieving pointer's is also known as dereferencing pointer.

If we change *p we also change x.

We can also assign the value that *p points to a different variable too (effectively changing the value of x):

How to change values using pointers

When we point a pointer to an array, it will point to the memory address of array's first item at index 0:

The pointer behaves in the same way as if were making the changes to the array:

How to move pointer to a different memory address

In this example, I pointed p to A's memory address and then pointed p to n's memory address and that's fine:

Let's uncomment last line so we can see that we can't do the same with arrays, i.e. re-assigning values:

Hope that clarifies a bit of the mystery behind pointers.