Adding linear linked list capability to an existing program.

[rylarson]

For my final program for my CS class, I am supposed to convert this program I already wrote which is basically an electronic journal to store the journal entries in a linear linked list and output them from that list.

I am having problems because we learned some linear linked list stuff, but we didnt really do anything related to this and thus far, I have not been able to do much with it. Here is my code, any help is MUCH appreciated. I am guessing I need to create a list class....but i dont really know how to go about it.

Header file

//jounral.h
#include<iostream>
using namespace std;
#include<cstring>

const int DATE = 11; //const int for the date
const int SUB = 51; //const int for the subject
const int MAX = 2000; //const int for the TEMP ENTRY

struct entry
{
       char date[DATE]; //array for holding the date
       char subject[SUB]; //array for holding the subject
       char *entry; //dynamic array for holding the journal entry
};
       
class journal
{
      public:
             journal(int size);  //constructor with argument for size
             ~journal();  //destructor
             void menu();             //menu function
             void new_entry();  //create a new Journal Entry
             void display_all(); //display all of the entries
             void search(); //find an entry based on subject
      private:
              entry *my_journal;//dynamic array for the number of entries
              int my_journal_size; //int for holding the size of the jounral
              int num_entries; //keeps track of the number of entries
};
              
void welcome(); //prototype for the welcome function
void termination(); //termination function
journal object(1); //initialize the class 

Here is the main code:

#include"journal.h"

int main()
{
    welcome();//calls the welcome function
    object.menu();//calls the menu function
    termination();//calls the termination function
}

void welcome()
{
     cout<<"Welcome to the Electronic Journal Program!" <<endl <<endl;
     cout<<"This program will allow you to record your" <<endl;
     cout<<"thoughts electronically instead of wasting"<<endl;
     cout<<"all of that paper!" <<endl <<endl;
}
journal::journal(int size = 100)
{
     my_journal = new entry[100];
     my_journal_size = 100;
     num_entries = 0;
}
journal::~journal()
{
     delete [] my_journal;
     my_journal = NULL;
}
void journal::menu() //menu function
{
     char choice; //variable to hold the choice
     
     do //loop that keeps prompting the user until a valid choice is inputted
     {
     cout<<"What would you like to do? " <<endl;
     cout<<"Choose Option 1 to add a new Journal Entry " <<endl;
     cout<<"Choose Option 2 to display all of your Journal Entries " <<endl;
     cout<<"Choose Option 3 to find an entry by the subject " <<endl <<endl;
     cout<<"Please enter a choice (1,2, or 3): " <<endl;
     
     cin>>choice; cin.ignore(100, '\n'); //reads in the choice and eats the rest
     if (choice == '1')
        object.new_entry(); //if 1, Create a new journal entry
     else if (choice == '2')
        object.display_all();// if 2, Display everything
     else if (choice == '3')
        object.search(); //if 3, search by subject
     else
         cout<<"Error, Please try again" <<endl <<endl; //error message, restarting the loop
     }while (choice != '1' && choice != '2' && choice != '3');
     
}
void journal::new_entry() //function for inputting a new journal entry
{
     
     char temp[MAX]; //variable to read in the journal entry temporarily
     
     //loop to read in until we reach the maximum size of the Journal
     while (num_entries > my_journal_size);
     {
     cout<<"Please enter the date for this entry (MM/DD/YYYY): ";
     cin.get(my_journal[num_entries].date, DATE, '\n'); //read in the date
     cin.ignore(100, '\n'); //eat the carriage return
     
     cout<<"Please enter the subject for this entry ";
     cin.get(my_journal[num_entries].subject, SUB, '\n'); //read in subject
     cin.ignore(100, '\n'); //eat the carriage return
     
     cout<<"Please enter your Journal entry ";
     cin.get(temp, MAX, '\n'); //read in the entry
     cin.ignore (100, '\n'); //eat the carriage return
     
     my_journal[num_entries].entry = new char[strlen(temp)+1]; 
     //creates an array of 1+the string length
     
     strcpy(my_journal[num_entries].entry, temp); //copy the temp into entry
     ++num_entries; //add 1 to the counter
     cout<<endl <<endl <<endl;
     menu();//calls the menu function to get back 
     }
}
void journal::display_all() //display everything entered
{ 
     for (int i = 0; i < num_entries; ++i) //loop that displays everything entered
     {   //output
         cout<< "Date: " << my_journal[i].date  <<endl;
         cout<< "Subject: " << my_journal[i].subject  <<endl <<endl;
         cout<< "Journal Entry: " <<endl << my_journal[i].entry <<endl <<endl;
     }
     menu();
}
void journal::search()//function to search by subject
{
     char query[100]; //Variable to hold the search query
     
     cout<< "What subject would you like to search for?: "; //Prompt user 
     cout<< endl <<endl;
     cin.get(query, 100, '\n'); cin.ignore (100, '\n'); //Read in the query
     
     for (int i = 0; i < num_entries; ++i)
     {
         if(strcmp(query, my_journal[i].subject) == 0)//Compare..MATCH!
         {    //output            
              cout<< "Date: " << my_journal[i].date  <<endl;
              cout<< "Subject: " << my_journal[i].subject  <<endl <<endl;
              cout<< "Journal Entry: " <<endl << my_journal[i].entry <<endl;
              cout<< endl;
         }
     }
     menu();
     
}
void termination()
{
     cout<< "Thank you for using the Electronic Journal!" <<endl;
     cout<< "Press ENTER to exit! ";
}

[Galik]

A linked list is where you store a pointer to the next entry in each record:

struct entry
{
       entry* next;  // link to next entry in the journal

       char date[DATE];
       char subject[SUB];
       char *entry; // same name?
};

So instead of storing your entry objects in an array like this:

entry* my_journal = new entry[100]; 

They want you to store them as a list of linked records.

entry* my_journal = 0; // initialise my_journal list  

You then need to write routines to add and delete items from that list

void journal::add_entry(entry* e)
{
       e->next = my_journal; // point this entry's next element to the current list
        my_journal = e; // make this entry the first in the list.
}

You need to do some reading on linked lists:

This tutorial seems quite good:

http://cslibrary.stanford.edu/103/LinkedListBasics.pdf

[rylarson]

OK, we actually did learn about LLL, we just never saw a complete program and were just taught the basics and expected to cram them into the existing program posted above. The tutorial still helped though. I am getting all sorts of errors and Im also not sure if I have the List structure set up correctly in the add_entry function (the loop obviously is not going to work, its just hanging around from the last program) Where should I go from here?

//Program 5

#include <iostream>
using namespace std;
#include <cstring>

const int DATE = 11; //const int for the date
const int SUB = 51; //const int for the subject
const int MAX = 2000; //const int for the TEMP ENTRY

struct journal_entry  //structure for the journal entry
{
       char date[DATE]; //array for holding the date
       char subject[SUB]; //array for holding the subject
       char *entry; //dynamic array for holding the journal entry
};

struct node  //structure for the node (data and pointer)
{
       journal_entry *data;  //instance of the journal struct
       node *next; //pointer to the next node
};

class list    //list class to manage the LLL
{
  public:
         list();  //constructor
         ~list(); //destrutor
        void add_entry(); 
        void display_all(node* head);
        void search();
        void menu();  //menu function prototype
  private:
        node* head;
        int my_journal_size; //int for holding the size of the jounral
        int num_entries; //keeps track of the number of entries
};      
    
void welcome();  //welcome function prototype

list object;  //initalize the class

int main()
{
    welcome();
    cin.get();
}
void welcome()
{
     cout<<"Welcome to the Electronic Journal Program!" <<endl <<endl;
     cout<<"This program will allow you to record your" <<endl;
     cout<<"thoughts electronically instead of wasting"<<endl;
     cout<<"all of that paper!" <<endl <<endl;
}
void list::menu() //menu function
{
     char choice; //variable to hold the choice
     head = new node;
     
     do //loop that keeps prompting the user until a valid choice is inputted
     {
     cout<<"What would you like to do? " <<endl;
     cout<<"Choose Option 1 to add a new Journal Entry " <<endl;
     cout<<"Choose Option 2 to display all of your Journal Entries " <<endl;
     cout<<"Choose Option 3 to find an entry by the subject " <<endl <<endl;
     cout<<"Please enter a choice (1,2, or 3): " <<endl;
     
     cin>>choice; cin.ignore(100, '\n'); //reads in the choice and eats the rest
     if (choice == '1')
        object.add_entry(); //if 1, Create a new journal entry
     else if (choice == '2')
        object.display_all(head->data);// if 2, Display everything
     else if (choice == '3')
        object.search(); //if 3, search by subject
     else
         cout<<"Error, Please try again" <<endl <<endl; //error message, restarting the loop
     }while (choice != '1' && choice != '2' && choice != '3');
}
list::list()
{
     head = new node;
     head = NULL;
     my_journal_size = 0;
     num_entries = 0;
}

list::~list()
{    
     delete head;
}

void list::add_entry()
{
     char temp[MAX]; //variable to read in the journal entry temporarily
     
     
     //loop to read in until we reach the maximum size of the Journal
     while (num_entries > my_journal_size);
     {
     cout<<"Please enter the date for this entry (MM/DD/YYYY): ";
     cin.get(head->data.date, DATE, '\n'); //read in the date
     cin.ignore(100, '\n'); //eat the carriage return
     
     cout<<"Please enter the subject for this entry ";
     cin.get(head->data.subject, SUB, '\n'); //read in subject
     cin.ignore(100, '\n'); //eat the carriage return
     
     cout<<"Please enter your Journal entry ";
     cin.get(temp, MAX, '\n'); //read in the entry
     cin.ignore (100, '\n'); //eat the carriage return
     
     
     ++num_entries; //add 1 to the counter
     
     cout<<endl <<endl <<endl;
     
     node* current = head;
     head = new node
     head->data = new journal_entry;
     head->data->entry = new char[strlen(temp)+1];
     strcpy(head->data->title, temp);
     head->next = current;
     }                
}

void list::display_all(node* head)
{
     if(head)
     {
			cout<<head->data.datedate;
			cout<<endl <<endl;
			cout<<head->data.subject;
			cout<<endl <<endl;
			cout<<head->data->entry
			
			display_all(head->next);
      }
}

void list::search()
{
            cout<<"SEARCH!";  
}