Lesson 6: An introduction to pointers

				

Welcome to the sixth in my series of tutorials.  This is one about a topic that you may or

may not have already heard about...pointers.  What are they, what do they do, why do we

care? First, why do we care.



We care about pointers because they allow access to memory, the also make array-access

faster, they are also somewhat necessary to understand some functions.  Most importantly,

you will see them a lot in other people's code.  You may not need to use them much, but it

will be tremendously important to understand them.



Second, what do they do.  Well, I might as well address this issue as well as what they are

at the same time.  Pointers are what they sound like...pointers.  They point to locations

in memory.  Picture this: a big jar that holds one thing, the name of another jar.  In the

other jar is the value of an integer.  The jars are memory locations.  The jar that holds

the name of the other jar is a pointer.  It points to the other drawer.



How can you use this?  Well, look at this little piece of code:



#include <iostream.h>



void main()

{

  int x;

  int *pointer;

  pointer=&x;  

  cin>>x;

  cout<<*pointer;

}



Guess what!  The cout outputs the value in x.  Why is that?  Well, look at the code.  The

integer is called x.  Then a pointer to an integer is defined as pointer.  The astrick(*)

symbol means that it is a pointer.  Then I give the memory location of x to pointer by

using the ampersand(&) symbol.  It gives the memory location of the variable it is in front

of.  For example, if the jar that had an integer had a ampersand in it it would output its

name, or location.



Then the user inputs the value for x.  Then the cout uses the * to put the value stored in

the memory location of pointer.  Huh?  Picture the jars again.  If the jar with the name of

the other jar in it had a * in front of it it would give the value stored in the jar with

the same name as the one in the jar with the name.  It's not too hard, the * gives the

value in the location.  The unastricked gives the memory location.

	

I hope this has been at least an interesting introduction to pointers.  I do not suggest

that you play around with them too much as you can do unpleasant things on your computer,

but you now should have a better understand of what they are.



Note: My homepage is http://www.cprogramming.com.  My email is lallain@concentric.net.  Please

email me with comments and or suggestions.  If you want to use this on your own site please

email me and add a link to http://www.cprogramming.com.  Thanks :)