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Shell Sorting a doubly linked list

Cr1ms0nStraY (3)
I got this project to create a doubly linked list from a file and sort it via the Shell sorting method. I think I figure it out (the logic behind the algorithm and how it works), and it really does sort the numbers I'm putting in the list without any errors, but I really need to be sure if I did it right. The function that I'm concerned about is ShellSort(). So here is the code:
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#include <iostream>
#include <ctime>
#include <fstream>
#include <string>
using namespace std;

const int N=10;

struct node
{
    int data;
    node* next;
    node* prev;
}
*head = NULL;

void addNode(int x)
{
    node *p=head, *q;
    q=new node;
    q->data=x;
    q->next=NULL;
    if (head)
    {
        while(p->next)
            p=p->next;
        p->next=q;
    }
    else
        head=q;
    q->prev=p;
}

int CreateFile ()
{
    int num[N];
    ofstream file1;
    file1.open("Numbers1.txt");
    if (file1.fail())             
    {
        cout<<"Error opening the file"<<endl;
        return 1;
    }
    cout<<"Enter 10 numbers (will be stored to a file): "<<endl;
    for(int i=0;i<N;i++)
    {
        cin>>num[i];
        file1<<num[i]<<endl;
    }
    cout<<endl;
    cout<<"The numbers were succsessfully stored to a text file (Numbers1.txt)"<<endl;
    file1.close();
    return 0;
}

void CreateListFromFile()
{
    int b=0;
    ifstream file2;
    file2.open("Numbers1.txt");
    if (file2.is_open())
    {
        while(file2>>b)
        {
            addNode(b);
        }
    }
        file2.close();
}
void ShowList(node *head)
{
    node *temp = head;
    while(temp != NULL)
    {
        cout<< temp->data<<" ";
        temp = temp->next;
    }
    cout<<endl;
}

void ShellSort()
{
    if(head)
    {
        int step=0;
        int lenght=0;
        node *p=head;
        while(p)
        {
            lenght++;
            p=p->next;
        }
        while(2*(3*step+1)<=lenght)
            step=3*step+1;
        for(step;step>0;step/=3)
            for(int i=step;i>0;i--)
                for(int j=step-i; j<lenght; j+=step)
                {
                    p=head;
                    int k;
                    for(k=0;k<j;k++)
                        p=p->next;
                    node* c=p;
                    int temp=k+step;
                    while(c)
                    {
                        for(k;k<temp;)
                            if(c)
                            {
                                k++;
                                c=c->next;
                            }
                            else break;
                            if(c)
                                if(p->data>c->data)
                                {
                                    int t=p->data;
                                    p->data=c->data;
                                    c->data=t;
                                }
                                temp+=step;
                    }
                }
    }
    cout<<"Sorting is done"<<endl;
}



void main()
{
    CreateFile();
    CreateListFromFile();
    ShellSort();
    ShowList(head);
}
Cr1ms0nStraY (3)
bump ...
Cr1ms0nStraY (3)
Still waiting for backup.
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