HELP Implementing Double Linked Lists as an Array of Pointers in C++
Hi Everyone,
I am studying/writing/ code for a future Advanced Data Structure class in C++; however I am not suppose to use STL, Templates and etc (the way I just code "kinda" of resembles what I have to use).
My application is suppose to read/analyze all integers contained in a text file of 5-digit integers (10000 – 99999).
For simplicity I am using the following input (or please, check the attached):
20007 20008 20009
20010 20010
20012 20012
20013
20014 20010
20015
20016
10000 10009 10009 10003
10004 10005
10006 10002
10008 10003
10007
10013
20151 20151
20152
30734
30735
30736
30736 30738
30738
30739
30740
30741
30742
30743 30744 30745 30746 30747
30748
So far, my code is not displaying/printing the lists separated by the first digit of these 5-digits integers. I am expecting it to display/print logically/similar to the following:
Output:
Results for input file numbers.txt:
27 total integers read from file
The 3 unique integers beginning with digit 1 were
18399 17342 19948
The 6 unique integers beginning with digit 3 were
39485 34710 31298 38221 35893 32791
The 4 unique integers beginning with digit 4 were
43928 49238 45678 43210
The 6 unique integers beginning with digit 6 were
64545 62987 66221 61777 66666 65432
The 2 unique integers beginning with digit 8 were
88888 86861
The 1 unique integer beginning with digit 9 was
98765
There were 22 unique 5-digit integers in the file.
The highest unique count in one list was 6 integers.
My code that will follow soon displays/prints only the LAST 5-digits "group" of integers (in this case the 5-digits starting with 3). I am not sure what's wrong with my code; perhaps I am not designing it correctly. May be my calls in it are on the wrong place or I have to write all integers and then traverse it and output it (if that's the case, I am not sure how).
Please, any directions, any ideas will be greatly appreciated.
My code follows:
**********************************************
Code:
#include <iostream>
#include <fstream>
#include <iomanip>
using namespace std;
const int MAX_CELLS = 10;
const int UNIQUE_FIVE_DIGIT = 5;
struct node
{
node* prev;
node* next;
int data;
};
/////////////////////////////////////////////////////////////////////
int main(int argc, char* argv[])
{
ifstream inFile;
node *lists[MAX_CELLS] = { NULL };
int count = -1;
bool result = true;
do
{
if ( argc != 2 )
{
cout << "Command line arguments not valid!" << endl << endl;
result = false;
}
if ( !argv[1] )
{
cout << "The command line arguments does not specify any filename!" << endl;
result = false;
}
inFile.open(argv[1]);
if ( !inFile )
{
cout << "The input data file does not exist or cannot be opened!" << endl;
result = false;
}
if ( result )
{
cout << "Results for input file " << argv[1] << ":" << endl;
ReadInFile(inFile, lists, count);
result = false;
}
} while ( result );
system("PAUSE");
return 0;
}
///////////////////////////////////////////////////////////////////
void ReadInFile(ifstream& inFile, node* arrayPtr[], int& count)
{
int number = 0;
int newNumber = 0;
int countResult = 0;
node* p = new node;
while ( inFile )
{
inFile >> number;
newNumber = number / 10000;
if ( !isDuplicate(arrayPtr[newNumber], number) )
{
arrayPtr[newNumber] = prepend( arrayPtr[newNumber], number );
p = arrayPtr[newNumber];
}
count++;
}
for (int count = 0; count < 10; count++)
{
arrayPtr[count] = p;
countResult = counting(p);
}
cout << setw(7) << count << " total integers read from file" << endl << endl;
inFile.close();
cout << "The " << countResult << " unique integers beginning with digit " << newNumber <<" were " << endl;
displayIt(p, countResult);
}
/////////////////////////////////////////////////////////////////////
void displayIt(node* p, int count)
{
cout << setw(14);
print_list(p);
cout << endl;
}
/////////////////////////////////////////////////////////////////////
bool isDuplicate(node* top, int number)
{
while( top != NULL )
{
if( top->data==number )
return true;
top = top->next;
}
return false;
}
/////////////////////////////////////////////////////////////////////
node* prepend(node* beginning, int number)
{
node* p = new node;
p->data = number;
p->prev = NULL;
p->next = beginning;
if( beginning != NULL )
{
beginning->prev = p;
}
return p;
}
/////////////////////////////////////////////////////////////////////
void print_list( node* beginning )
{
for( node *p=beginning; p != NULL; p=p->next )
{
std::cout << p->data;
if( p->next != NULL )
{
std::cout << " ";
}
}
}
/////////////////////////////////////////////////////////////////////
int counting( node* beginning )
{
int count(0);
for( node *p=beginning; p != NULL; p=p->next )
{
++count;
}
return count;
}
**********************************************
Big thanks in advance.
Marco
Re: HELP Implementing Double Linked Lists as an Array of Pointers in C++
Quote:
Originally Posted by
lanza
I am not sure what's wrong with my code; perhaps I am not designing it correctly. May be my calls in it are on the wrong place or I have to write all integers and then traverse it and output it (if that's the case, I am not sure how).
Honestly, there should be no "maybes" when you write the code. Everything you code must be done with certainty that what you have written will execute properly. Everything you design must be done with complete confidence that the design works -- first on paper, and then translated to programming code.
Of course, if the code doesn't execute properly (which is more often than not), then you debug the code using the debugger or whatever other technique (print statements, etc.) to find out where the code deviates from your initial plans. Then you fix the code according to what you've discovered by debugging, or you redo your design based on what you've discovered by debugging. That is how programming works, whether it is student or professional.
Quote:
Please, any directions, any ideas will be greatly appreciated.
Given what was stated, have you debugged your own code?
Regards,
Paul McKenzie
Re: HELP Implementing Double Linked Lists as an Array of Pointers in C++
Hi Paul,
Big thanks for the reply.
I used the debugger and so far follows most of my design (but not sure how to display all data yet):
1) I read the data file and while it is reading it
2) check for duplicates
3) if it's not a duplicate then I will add into the lists based on the first digit
4) then I counted and display it, HOWEVER
it is displaying the last 5-digit integers (starting with digit 3) as follows:
Results for input file 1numbers.txt:
43 total integers read from file
The 14 unique integers beginning with digit 3 were
30748 30747 30746 30745 30744 30743 30742 30741 30740 30739 30738 30736
30735 30734
Press any key to continue . . .
However, I am expecting it to display all data from the file (in my case I have digits starting with 1, 2, and 3 as you can see in my first/previous post).
It's doing most of it but I was expecting it to display the other unique integers with digit 2 and ... with digit 1 as well since it is in the input file.
I am not sure yet why.
Big thanks.
Marco
Re: HELP Implementing Double Linked Lists as an Array of Pointers in C++
Quote:
Originally Posted by
lanza
It's doing most of it but I was expecting it to display the other unique integers with digit 2 and ... with digit 1 as well since it is in the input file.
I am not sure yet why.
So you should go straight to the function that prints:
Code:
void print_list( node* beginning )
{
for( node *p=beginning; p != NULL; p=p->next )
{
std::cout << p->data;
if( p->next != NULL )
{
std::cout << " ";
}
}
}
If you claim that you don't see all your output, the only conclusion is that "p" no longer points to the beginning of your list of nodes.
This is what I mean by debugging -- somewhere along the way, you've either lost track, replaced, or did something that causes the list to either lose its contents, or you've moved the head of the list around and now it points somewhere else. How else would a seemingly simple print loop not print out the correct results, unless "beginning" has been trashed somewhere?
So use the debugger, keep track to make sure what is happening to "beginning" to see where it goes wrong.
Regards,
Paul McKenzie
Re: HELP Implementing Double Linked Lists as an Array of Pointers in C++
Topic number 1 in schools really should be how to use the debugger and why you can't write any code without it. You've made the classic beginner mistake of trying to write the whole program at once and now you have to figure out which part is broken. Any of us would write one small part at a time, step through it in the debugger to make sure it's doing what we want it to, then moving on to the next part. What you need to do now is step through all your code. Make sure the nodes are being created and inserted correctly, make sure you dupe test is working correctly, then make sure you're outputting correctly. Your mistake could be anywhere. You need to debug individual functions as you go so that when something goes wrong, it's pretty easy to identify.
Re: HELP Implementing Double Linked Lists as an Array of Pointers in C++
Big Thanks for all of you.
Problem solved; now I just need to figure out how this program will produce the last line of the sample output such as "The highest unique count in one list was 6 integers". In other words, what list has the highest values in it.
Thanks.
Marco
Re: HELP Implementing Double Linked Lists as an Array of Pointers in C++
Quote:
Originally Posted by
GCDEF
Topic number 1 in schools really should be how to use the debugger and why you can't write any code without it.
I disagree. Real programmers don't use debuggers. They write correct code. And they use the Stepwise Refinement method to accomplish that.
Debuggers are fine when you inherit a pile of crap code and need to quickly hide the bad smell. But when you write new code it should work from start to finish and you should be confident it does.
In this case the OP should start all over and develop the code incrementally in small working steps one by one. Start with something working and make sure everything you add in works too. How hard is that really?
Re: HELP Implementing Double Linked Lists as an Array of Pointers in C++
Quote:
Originally Posted by
nuzzle
I disagree. Real programmers don't use debuggers. They write correct code. And they use the Stepwise Refinement method to accomplish that.
Debuggers are fine when you inherit a pile of crap code and need to quickly hide the bad smell. But when you write new code it should work from start to finish and you should be confident it does.
In this case the OP should start all over and develop the code incrementally in small working steps one by one. Start with something working and make sure everything you add in works too. How hard is that really?
I really hope you're joking.
Re: HELP Implementing Double Linked Lists as an Array of Pointers in C++
Quote:
Originally Posted by
GCDEF
I really hope you're joking.
No I don't.
It's much better to avoid errors than to look for them later.
Re: HELP Implementing Double Linked Lists as an Array of Pointers in C++
Quote:
Originally Posted by
nuzzle
No I don't.
It's much better to avoid errors than to look for them later.
I don't know of any programmers that write perfect code on the first try every time, and I don't know of any programmers that can look at code and be absolutely positive what it's doing every time. What I'm saying, is write a small section of code, run it in the debugger to be sure it works then move on to the next piece. Proper use of the debugger is the way to avoid errors.
Re: HELP Implementing Double Linked Lists as an Array of Pointers in C++
Quote:
Originally Posted by
nuzzle
I disagree. Real programmers don't use debuggers. They write correct code. And they use the Stepwise Refinement method to accomplish that.
Debuggers are fine when you inherit a pile of crap code and need to quickly hide the bad smell. But when you write new code it should work from start to finish and you should be confident it does.
In this case the OP should start all over and develop the code incrementally in small working steps one by one. Start with something working and make sure everything you add in works too. How hard is that really?
The best and most reliable method of achieving this "stepwise refinement" is stepping through your code in a debugger and verifying that it does indeed work as you intended.
