doubly linked lists

This is a discussion on doubly linked lists within the C++ Programming forums, part of the General Programming Boards category; I am trying to work with a doubly linked list. The best example that I could understand was from a ...

  1. #1
    Registered User
    Join Date
    Feb 2002
    Posts
    5

    Angry doubly linked lists

    I am trying to work with a doubly linked list. The best example that I could understand was from a C book. I attempted to convert that example to a functional C++ program.

    My limited knowlege of linked lists may have let me astray. But here goes. My program compiles but I do not get the menu.

    When I press enter then the menu comes up, but It is not responding to my input. I think my error is with thet gets and the fgets. I read that C++ accepts the gets and fgets syntax with stdio.h header. I am not sure what I need to do to make it work in C++.

    Any help is appreciated. I think I applied the code tags correctly in my program. If not, I appoligize. I sincerely tired to make the program code easier to read.

    The output is suppose to look like.

    1. Enter a name
    2. Delete a name
    3. List the file
    4. Search
    5. Save the file
    6. Load the file
    7. Quit

    Enter your choice: 1
    Enter name: Jim Black
    Enter street: 258 Nowh
    Enter city: Duno
    Enter state: CA
    Enter zip: 258913
    Enter name:
    1. Enter a name
    2. Delete a name
    3. List the file
    4. Search
    5. Save the file
    6. Load the file
    7. Quit

    Enter your choice:

    // My listed list program
    #include <stdio.h> //
    #include <stdlib.h> // For atoi function
    #include <string.h> // for strcmp function
    #include <iostream.h>

    struct address
    {
    char name[30];
    char street[40];
    char city[20];
    char state[3];
    char zip[11];
    struct address *next; // pointer to next entry
    struct address *prior; // pointer to previous record
    };

    struct address *start; // pointer to first entry in list
    struct address *last; // pointer to last entry
    struct address *find(char *);

    void enter(void), search(void), save(void);
    void load(void), list(void);
    void mldelete(struct address **, struct address **);
    void dls_store(struct address *i, struct address **start,
    struct address **last);
    void inputs(char *, char *, int), display(struct address *);
    int menu_select(void);

    int main(void)

    {
    start = last = NULL; // initialize start and end pointers

    for(;;) // Forever
    {
    switch(menu_select())
    {
    case 1: enter(); // enter an address
    break;
    case 2: mldelete(&start, &last); // remove an address
    break;
    case 3: list(); // display the list
    break;
    case 4: search(); // find an address
    break;
    case 5: save(); // save list to disk
    break;
    case 6: load(); // read from disk
    break;
    case 7: exit(0);
    }
    }
    return 0;
    }

    // Select an operation.

    int menu_select(void)
    {
    char s[80];
    int c;

    cout <<endl;
    cout << "1. Enter a name\n";
    cout << "2. Delete a name\n";
    cout << "3. List the file\n";
    cout << "4. Search\n";
    cout << "5. Save the file\n";
    cout << "6. Load the file\n";
    cout << "7. Quit\n";
    do
    {
    cout << "\nEnter your choice: ";
    gets(s);
    c = atoi(s);
    } while(c<0 || c>7);
    return c;
    }

    // Enter names and addresses.

    void enter(void)
    {
    struct address *info;

    for(;;) {
    info = (struct address *)malloc(sizeof(struct address));
    if(!info) {
    cout <<"\nout of memory";
    return;
    }

    inputs ("Enter name: ", info->name, 30);
    if(!info->name[0]) break; // stop entering
    inputs ("Enter street: ", info->street, 40);
    inputs ("Enter city: ", info->city, 20);
    inputs ("Enter state: ", info->state, 3);
    inputs ("Enter zip: ", info->zip, 10);

    dls_store(info, &start, &last);
    } // entry loop
    }

    // This function will input a string up to
    // the length in count and will prevent
    // the string from being overrun. It will also
    // display a prompting message.

    void inputs(char *prompt, char *s, int count)
    {
    char p[255];

    do
    {
    cout << prompt;
    fgets(p, 254, stdin); // look at this //
    if(strlen(p) > count) cout << "\nToo Long\n";
    }
    while(strlen(p) > count);

    p[strlen(p)-1] = 0; // remove newline character
    strcpy(s, p);
    }

    // Create a doubly linked list in sorted order.

    void dls_store
    (
    struct address *i, // new element
    struct address **start, // first element in list
    struct address **last // last element in list
    )
    {
    struct address *old, *p;
    if(*last==NULL)
    { // first element in list
    i->next = NULL;
    i->prior = NULL;
    *last = i;
    *start = i;
    return;
    }
    p = *start; // start at top of list
    old = NULL;
    while(p)
    {
    if(strcmp(p->name, i->name)<0)
    {
    old = p;
    p = p->next;
    }
    else
    {
    if(p->prior)
    {
    p->prior->next = i;
    i->next = p;
    i->prior = p->prior;
    p->prior = i;
    return;

    }
    i->next = p; // new first element
    i->prior = NULL;
    p->prior = i;
    *start = i;
    return;

    }
    }
    old->next = i; // put on end
    i->next = NULL;
    i->prior = old;
    *last = i;
    }

    // Remove an element from the list.
    void mldelete(struct address **start, struct address **last)
    {
    struct address *info;
    char s[80];

    inputs("Enter name: ", s, 30);
    info = find(s);
    if(info)
    {
    if(*start==info)
    {
    *start=info->next;
    if(*start) (*start)->prior = NULL;
    else *last = NULL;
    }
    else
    {
    info->prior->next = info->next;
    if(info!=*last)
    info->next->prior = info->prior;
    else
    *last = info->prior;
    }
    free(info); // return memory to system
    }

    }

    // Find an address.
    struct address *find( char *name)
    {
    struct address *info;
    info = start;
    while(info)
    {
    if(!strcmp(name, info->name)) return info;
    info = info->next; // get next address
    }
    cout << "Name not found.\n";
    return NULL; // not found
    }

    // Display the entire list.
    void list(void)
    {
    struct address *info;

    info = start;
    while(info)
    {
    display(info);
    info = info->next; // get next address
    }
    cout << "\n\n";
    }

    // This function actually prints the fields in each address.

    void display(struct address *info)
    {
    cout << info->name;
    cout << info->street;
    cout << info->city;
    cout << info->state;
    cout << info->zip;
    cout << endl << endl;
    }

    // Look for a name in the list.
    void search(void)

    {
    char name[40];
    struct address *info;

    cout << "Enter name to find: ";
    gets(name);
    info = find(name);
    if(!info)
    cout << "Not Found" << endl;
    else display(info);
    }

    // Save the file to disk.

    void save(void)

    {
    struct address *info;

    FILE *fp;

    fp = fopen("mlist", "wb");
    if(!fp)
    {
    cout << "Cannot open file.\n";
    exit(1);
    }
    cout << "\nSaving File\n";

    info = start;
    while(info)
    {
    fwrite(info, sizeof(struct address), 1, fp);
    info = info->next; // get next address
    }
    fclose(fp);
    }

    // Load the address file.

    void load()

    {
    struct address *info;
    FILE *fp;
    {

    fp = fopen("mlist", "rb"); // open binary file for update // reading & writing.
    if(!fp)
    {
    cout << "Cannot open file.\n";
    exit(1);
    }

    // free any previously allocated memory

    while(start)

    {
    info = start->next;
    free(info);
    start = info;
    }

    // reset top and bottom pointers

    start = last = NULL;
    cout <<"\nLoading File\n";
    while(!feof(fp))
    {
    info = (struct address *) malloc(sizeof(struct address));
    if(!info)
    {
    cout << "Out of Memory";
    return;
    }
    if(1 != fread(info, sizeof(struct address), 1, fp)) break;
    dls_store(info, &start, &last);
    }
    fclose(fp);
    }

  2. #2
    Unregistered
    Guest
    Should had done the adventure game if you are who I think you are.......

    Becareful cause doing a doubly might raise an eyebrow with him.....

  3. #3
    Unregistered
    Guest

    Thumbs up Try this.......

    Copy and paste this in for main.
    See what you get.....


    int main(void)
    {
    // char s[80];
    int Response = -1;
    cout << "Lunch Order" << endl;

    while(Response !=1)
    {
    cout << "1. Enter a name\n";
    cout << "2. Delete a name\n";
    cout << "3. List the file\n";
    cout << "4. Search\n";
    cout << "5. Save the file\n";
    cout << "6. Load the file\n";
    cout << "7. Quit\n";
    cin >>Response;

    /* do {
    cout << "\nEnter your choice: ";
    gets(s);
    c = atoi(s);
    } while(c<0 || c>7);
    return c; */

    start = last = NULL; /* initialize start and end pointers */

    for(;
    {
    switch(Response)
    {
    case 1: enter(); /* enter an address */
    break;
    case 2: mldelete(&start, &last); /* remove an address */
    break;
    case 3: list(); /* display the list */
    break;
    case 4: search(); /* find an address */
    break;
    case 5: save(); /* save list to disk */
    break;
    case 6: load(); /* read from disk */
    break;
    case 7:
    cout << "Thanks anyway";
    system("PAUSE");
    exit(0);
    // break;
    } return 0;
    }
    }
    }

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