Pointers

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From the course by Duke University

Pointers, Arrays, and Recursion

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Duke University

Pointers, Arrays, and Recursion

64 ratings

Course 3 of 4 in the Specialization Introduction to Programming in C

The third course in the specialization Introduction to Programming in C introduces the programming constructs pointers, arrays, and recursion. Pointers provide control and flexibility when programming in C by giving you a way to refer to the location of other data. Arrays provide a way to bundle data by guaranteeing sequences of data are grouped together. Finally, recursive functions—functions that call themselves—provide an alternative to iteration that are very useful for implementing certain algorithms.

From the lesson

Pointers

Pointers are one of the most important and powerful aspects of the C language. Pointers are critical to understanding arrays, which let you manipulate sequences of data. They also give a programmer control and flexibility when programming, enabling solutions that are clean and efficient. Some other languages use pointers implicitly—or pointer-like constructs—so understanding their use will make you a better programmer in any language.

Corrected Swap2:38

Meet the Instructors

Andrew D. Hilton
Associate Professor of the Practice
Electrical and Computer Engineering
Anne Bracy
Senior Lecturer
Computer Science, Cornell University
Genevieve M. Lipp
Adjunct Professor
Electrical and Computer Engineering/Mechanical Engineering
Liz Wendland

In this video, we're going to step through some code that

uses pointers to show you how to best draw diagrams,

to understand what is happening in a line by line fashion.

The first line of code declares a variable X and gives it an initial value of three.

The next line of code declares a variable P that is of type integer pointer.

It does not yet initialize it.

So, in the beginning we have a box,

but we don't yet know what's in the value.

But we do know that the box is called P. The next line of

code will initialize the value of P to have the value of the address of X.

When you see an assignment like this,

it's important to begin by looking at

the left side first and then look at the right side.

Looking at the left side we can see that the value is going to be placed into

the variable P. When we look on the right side of the assignment statement,

we see that the value we're going to place is the address of X.

So, when we execute this line,

we're going to change the variable P to now have an arrow that points to X.

On the next line,

on the left side we see the value that P points to,

which is actually the variable X,

we're going to set that to have the value on the right side which is four.

When we execute this line of code,

we're going to go to that which P points to,

and change that to have the value four.

The next line of code declares a variable Y,

and the value it's initialized to is the value P points to, in this case four.

When we execute this line of code,

we're going to create a new box named Y and give it the value four.

The next line is going to declare a variable of type integer pointer called Q,

and we're going to give it an initial value of the address of Y.

That means we're going to create a new box called Q,

and it's going to have an arrow in it that points to Y.

The next line is a little bit tricky.

On the left, we're going to be storing the value we create into that which Q points to,

namely the box for Y.

And the value that we're going to store there is that which P points to,

which is four plus one.

So, when we execute this line of code we're going to

take the value P points to, which is four,

add one to it, which is five,

and store that at the location Q points to,

namely the variable Y.

The final line of code we have simply gives the value of P to the variable Q. Q was

the receiving value and the value it's going to

get is the value P has, which has an arrow.

So, when we execute this line of code we're going to replace the value

of Q with an arrow that points to the thing P points to.

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