NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part2/12254

Text File | 1996-08-05 | 11.1 KB | 402 lines

Path: wilks.demon.co.uk!Ian
From: Ian M Wilks <[e-mail]>
Newsgroups: comp.lang.c
Subject: Re: Need a linked list program
Date: Fri, 29 Mar 1996 23:52:46 +0000
Organization: Ian
Distribution: world
Message-ID: <5N$[e-mail]>
References: <4jf76k$[e-mail]>
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In article <4jf76k$[e-mail]>, David <[e-mail]> writes
>Does anyone out there have a linked list program which moves in both
>directions and can also create, delete and search items in the list?
>
>I'm doing a study into data structures at the moment and this would
>really help.
>

Hope this helps.  Unfortunately, its in C++ but should point you in the
right direction:

#include <fstream.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <conio.h>
#define YES 1
#define NO 0

struct address
{
        char name[40];
        char street[40];
        char town[30];
        char county[30];
        char postcode[10];
        address * next;         //pointer to next entry
        address * previous;     //pointer to previous entry
};

address *start, *last;
fstream list_file;

address * find(char *);
void enter(), search(), save(), load(), list();
void delete_entry(address **, address **);
void store(address *, address **, address **);
void display(address *);
int select_menu();

void main()
{
        int another_go = YES;
        start = last = NULL;    //initialize first and last pointers

        while(another_go == YES)
        {
                switch(select_menu())
                {
                        case 1:
                                enter();        //enter data into list
                                break;
                        case 2:
                                delete_entry(&start, &last);
                                break;
                        case 3:
                                list();         //list the data
                                break;
                        case 4:
                                search();       //find a record
                                break;
                        case 5:
                                save();         //save list to disc file
                                break;
                        case 6:
                                load();      //load list from disc file
                                break;
                        case 7:
                                another_go = NO;
                                break;
                        default:
                                cout << "\n\nInternal Error\n\n";
                }               //end of switch statement
        }                       //end of while loop
}                               //end of main()

int select_menu()
{
        int item;
        clrscr();
        cout << endl << "\t 1\tMake Entry\n" << "\t 2\tDelete Entry\n"
                 << "\t 3\tList Entries\n" << "\t 4\tSearch\n"
                 << "\t 5\tSave to File\n" << "\t 6\tLoad from File\n"
                 << "\t 7\tExit from Program\n\n";
        do
        {
                cout << "\t\t\tEnter Choice:  ";
                cin >> item;
        }while(item < 0 || item > 7);
        return(item);
}

//Enter data into list
void enter()
{
        address * info;
        char again = 'Y';
        do
        {
                if(!(info = new address))
                {//check if memory allocated - if not terminate program
                        cout << "\n\nMEMORY ALLOCATION ERROR";
                        exit(-1);
                }
                clrscr();
                cout << "\n\tEnter Name:  ";
                gets(info->name);
                cout << "\n\tEnter Street:  ";
                gets(info->street);
                cout << "\n\tEnter Town:  ";
                gets(info->town);
                cout << "\n\tEnter County:  ";
                gets(info->county);
                cout << "\n\tEnter Postcode:  ";
                gets(info->postcode);

                store(info, &start, &last);     //put data into list

                cout << "\n\n\nEnter another?  (Y/N)   ";
                cin >> again;
        }while( again == 'Y' || again == 'y');
}

//create linked list
void store(address * i, address ** start, address **last)
{
        if (*start == NULL)     //first record has to be treated
        {                       //specially
                i->next = NULL;         //if first record - no next
                                        //record
                i->previous = NULL;     //if first record - no previous
                                        //record
                *last = i;              //store details in last
                *start = i;             //store details in start
        }
        else                            //not first record
        {
                (*last)->next = i;
                i->next = NULL;
                i->previous = *last;
                *last = i;
        }
}

//remove entry from list
void delete_entry(address ** start, address ** last)
{
        address * info;
        char name[40];

        clrscr();
        cout << "\n\n\t\tEnter Name:  ";
        gets(name);
        info = find(name);              //find record
        if(info)
        {
                if(*start == info)      //if start of list is to be
                                        //deleted
                {                       //new start of list is needed
                        *start = info->next;
                        if(*start)
                                (*start)->previous = NULL;
                        else
                                *last = NULL;
                }
                else
                {
                        info->previous->next = info->next;
                        if(info != *last)
                                info->next->previous = info->previous;
                        else
                                *last = info->previous;
                }
                delete info;
        }
        else
                gotoxy(25, 25);
        cout << "Press a key to continue.";
        getch();
}

//find address
address * find(char * name)
{
        address * info;

        info = start;

        while(info)
        {
                if(!strcmp(name, info->name))
                        return(info);
                info = info->next;
        }
        cout << "\n\n\tName not found\n";
        return(NULL);
}

//display list
void list()
{
        address * info;
        int count = 0;

        clrscr();
        info = start;

        while(info)
        {
                count++;
                display(info);
                info = info->next;

                if ( (count % 4) == 0)  //to prevent records scrolling
                                        //off screen
                {
                        gotoxy(25,25);
                        cout << "Press a key to continue";
                        getch();
                        clrscr();
                }
        }
        cout << endl << endl;
        gotoxy(25, 25);
        cout << "Press a key to continue.";
        getch();
}

//print list to screen
void display(address *info)
{
        cout << endl << "\t" << info->name << endl
             << "\t" << info->street << endl
             << "\t" << info->town << endl
             << "\t" << info->county
             << ", " << info->postcode << endl;
}

//look for name in list
void search()
{
        char name[40];
        address * info;

        clrscr();
        cout << "\n\nEnter name to find:  ";
        gets(name);

        info = find(name);

        if (info)
        {
                display(info);
                gotoxy(25, 25);
                cout << "Press a key to continue.";
                getch();
        }
        else
        {
                gotoxy(25, 25);
                cout << "Press a key to continue.";
                getch();
        }
}


//save list to disc
void save()
{
        address * info;

        rename("list.dat", "list.old");         //create backup file
        list_file.open("list.dat",ios::out);
        if(!list_file)
        {
                cout << "\n\nCould not open file.";
                exit(-1);
        }
        cout << "\n\n\t\tSAVING FILE\n";

        info = start;
        while(info)
        {
                list_file << info->name << endl << info->street << endl
                          << info->town << endl << info->county << endl
                          << info->postcode << endl;
                info = info->next;
        }
        list_file.close();
}

//load from disc
void load()
{
        address * info;

        list_file.open("list.dat", ios::in);
        if(!list_file)
        {
                cout << "\n\nCould not open file.";
                exit(-1);
        }

        while(start)    //delete any lists already in memory
        {
                info = start->next;
                delete info;
                start = info;
        }
        start = last = NULL;

        cout << "\n\n\t\tLOADING FILE\n";

        while(!list_file.eof())
        {
                info = new address;
                if(!info)
                {
                        cout << "\n\n\t\tMEMORY ALLOCATION ERROR\n";
                        exit(-1);
                }
                list_file.getline(info->name, 40);
                list_file.getline(info->street, 40);
                list_file.getline(info->town, 30);
                list_file.getline(info->county, 30);
                list_file.getline(info->postcode, 10);

                if(!( list_file.eof()))
                {
                        store(info, &start, &last);
                }
        }
        list_file.close();
}



// If you want to store the list in ascending order use this function
//instead:
/*
void store(address * i, address ** start, address ** last)
{
        address * old,  * point;

        if(*last == NULL)               //first element in list
        {
                i->next = NULL;
                i->previous = NULL;
                *last = i;
                *start = i;
                return;
        }

        point = *start;                 //start at top of list

        old = NULL;

        while(point)
        {
                if(strcmp(point->name, i->name) < 0)
                {
                        old = point;
                        point = point->next;
                }
                else
                {
                        if(point->previous)
                        {
                                point->previous->next = i;
                                i->next = point;
                                i->previous = point->previous;
                                point->previous = i;
                                return;
                        }
                        i->next = point;
                        i->previous = NULL;
                        point->previous = i;
                        *start = i;
                        return;
                }
        }
        old->next = i;
        i->next = NULL;
        i->previous = old;
        *last = i;
}
*/