• Marcus IkeaTheSofa (13/13) Mar 23 2005 Pointers point to an address in memory. You can store data in them like
• Heinz Saathoff (47/55) Apr 01 2005 Pointers are of great value when you have dynamic data structures such

Marcus IkeaTheSofa <ikea_the_Sofa hotmail.com> writes:

Pointers point to an address in memory. You can store data in them like 
standard variables. You can use the address or the actual data contained 
at the address.. my questions is, what do they let you do that is so 
great? I'm not sure at all what the added value is. I am very 
inexperienced as a programmer(obviously), so I was wondering if someone 
could explain it to me and/or show me an example or two (my book shows 
me how to use them and talks about how they are great and so on, but not 
really why they are great or how they would be used to make them great.)

Confused in Spokane....
-- 

Marcus Koontz
ikea_the_sofa _A T_ hotmail.com
“Be the change you want to see in the world”

Heinz Saathoff <hsaat despammed.com> writes:

Hello,

Marcus IkeaTheSofa wrote...
 Pointers point to an address in memory. You can store data in them like 
 standard variables. You can use the address or the actual data contained 
 at the address.. my questions is, what do they let you do that is so 
 great? I'm not sure at all what the added value is. I am very 
 inexperienced as a programmer(obviously), so I was wondering if someone 
 could explain it to me and/or show me an example or two (my book shows 
 me how to use them and talks about how they are great and so on, but not 
 really why they are great or how they would be used to make them great.)

Pointers are of great value when you have dynamic data structures such 
as lists or trees. You can allocate memory and store the address of the 
allocated memory area in a pointer. Here is a short example of a list:

   typedef int DATA;

   struct LIST_ELEMENT {
       LIST_ELEMENT  *next;    // next is a pointer!
       DATA   data;            // some data to store
   };

   LIST_ELEMENT *first=0;      // pointer to first Element
   LIST_ELEMENT *last=0;       // pointer to last Element
 
   void AppendData(DATA some_data)
   {
	// memory area is allocated by new, the address is store
	// in 'new_element'
       LIST_ELEMENT *new_element = new LIST_ELEMENT; 
      
       // fill in Data and initialize next
       new_element->data = some_data;
       new_element->next = 0;

       // now link in Element
	if(first == 0) {
          // List is empty
          first = new_element;
       }
       else {
          // list contains at least 1 Element
          // add new_element to the end
          last->next = new_element;
       }

       // make last point to last element
       // which is new_element
       last = new_element;
   }//end AppendData


   // traversing is easy now
   void PrintAll() 
   {
       for(LIST_ELEMENT *rpt=first; rpt!=0; rpt=rpt->next) {
          printf("val is %d\n", rpt->data);
       }
   }//end PrintAll



Lists are a classic example of dynamic data structures and should be 
included in most books that cover C and C++


HTH,
	Heinz