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143 New Member
OK, I'm wrking on this program. I need to create a linked list using pointers and dynamic variables. I have to read integers from a file...traverse the list...input an integers from the keyboard...then delete every number that is larger than the one from the keyboard....The n display all the remaining integers.

Here's what I have:

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  1. #include <iostream>
  2. #include <iomanip>
  3. #include <fstream>
  4.  
  5. using namespace std;
  6.  
  7. ifstream filein;
  8.  
  9. struct nodetype;    //forward, incomplete declaration
  10. typedef nodetype *nodeptrtype;
  11.  
  12. struct nodetype
  13. {
  14.     int num;
  15.     nodeptrtype ptr;
  16. };
  17. //main()***************************************************
  18. void main()
  19. {
  20.     filein.open("E:INTFILE.DAT");  //opens external file that contains several (28) random integers
  21.  
  22.     nodeptrtype front, auxptr, endptr, currentptr, previousptr;
  23.     int numin;
  24.     int sum = 0;
  25.  
  26.     filein>>numin;
  27. //this segment creates a linked list by placing each new mode
  28.     //at the end of the list
  29.         front = new nodetype;
  30.         front->num = numin;
  31.         front->ptr = NULL;
  32.         endptr = front;
  33.     do
  34.     {
  35.         filein>>numin;
  36.         if(filein)
  37.         {
  38.             auxptr = new nodetype;
  39.             auxptr->num = numin;
  40.             auxptr->ptr = NULL;
  41.             endptr->ptr = auxptr;
  42.             endptr = auxptr;
  43.         }
  44.     }while(filein);
  45.  
  46. //This segment traverses the linked list and displays the integers on one line
  47.     cout<<"Values in the first list: "<<endl;
  48.     auxptr = front;
  49.     while (auxptr != NULL)
  50.     {
  51.         cout<<auxptr->num<<" ";
  52.         auxptr = auxptr->ptr;
  53.     }
  54.     cout<<endl<<endl;
  55.  
  56. int hinum;
  57.  
  58.     cout<<"enter an integer.  All integers on the list higher than this number should be deleted  ";
  59.     cin>>hinum;
  60.     auxptr = front;                            //currentptr previousptr
  61.     while (auxptr != NULL)
  62.     {
  63.         if(auxptr->num > hinum)
  64.         {
  65.  
  66.             currentptr = auxptr;
  67.             delete currentptr;
  68.             auxptr = previousptr;
  69.  
  70.         }
  71.         else
  72.             previousptr = auxptr;
  73.  
  74.         cout<<previousptr->num<<" ";
  75.         auxptr = auxptr->ptr;
  76.     }
  77.     cout<<endl<<endl;
  78. }
Any help would be appreciated.
Dec 7 '06 #1
4 1164
DeMan
1,806 Top Contributor
Methinks this has been addressed elsewhere
Dec 7 '06 #2
teddarr
143 New Member
Same program........ a couple of steps farther down the line.

I have the steps you helped me with earlier working now.

Thank you
Dec 7 '06 #3
DeMan
1,806 Top Contributor
Sorry, I should look before making assumptions.... ..

int hinum;

cout<<"enter an integer. All integers on the list higher than this number should be deleted ";
cin>>hinum;
auxptr = front; //currentptr previousptr
while (auxptr != NULL)
{
if(auxptr->num > hinum)
{

currentptr = auxptr;
delete currentptr;
auxptr = previousptr;

}
else
previousptr = auxptr;

cout<<previousp tr->num<<" ";
auxptr = auxptr->ptr;
}
cout<<endl<<end l;
In your loop, if you have a number greater than the input you:
set currentptr to auxptr (correct)
delete currentptr (not entirely necessary, although there are some memory issues which we won't go into yet)

You should also:
previousptr->ptr=currentp tr->ptr (the previous ptr should now point to the element beyond the current ptr)
previousptr stays the same,
auxptr = previousptr->ptr

Notice: this doesn't actually delete the node, but it removes it from the list (and in fact, unless you know where it is in memory, you will never find it again), so for all intents and purposes it is gone.
Dec 7 '06 #4
teddarr
143 New Member
Thanks, That helps.

My instuctor has already touched on those "memory issues" so there's no need to get into that. I'm just getting a little confused with all these pointers going everywhere. As usual it's nothing I wont straighten out with some practice.

Thanks again for the help.
Dec 8 '06 #5

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