C++ linked list implementation multiple data insertion - c++

Question

I'm trying to create a subject pre-requisite checker using linked list. I know how to insert single data into a node.
My problem is how to insert multiple data into a node? I found a good example which fits my assignment perfectly. But the problem is I do not understand C very much. Can any one help to explain the void add() function below? I want to use that add function to my assignment.
#include <stdio.h>
#include <conio.h>
#include <malloc.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
struct node
{
char data [ 20 ];
char m [ 5 ] [ 20 ];
int mcount;
struct node * link;
};
struct node * dic [ 26 ];
void add ( char * );
int search ( char * );
void show( );
void deldic( );
void main( )
{
char word [ 20 ] , ch;
int i;
clrscr( );
while ( 1 )
{
clrscr( );
printf ( "\n\t\tDictionary\n" );
printf ( "\n\t\t1.Add Word.\n" );
printf ( "\t\t2.Search Word.\n" );
printf ( "\t\t3.Show Dictionary.\n" );
printf ( "\t\t0.Exit." );
printf ( "\n\n\t\tYour Choice ");
scanf ( "%d", &ch );
switch ( ch )
{
case 1 :
printf ( "\nEnter any word : " );
fflush ( stdin );
gets ( word );
add ( word );
break;
case 2 :
printf ( "\nEnter the word to search : " );
fflush ( stdin );
gets ( word );
i = search ( word );
if ( ! i )
printf ( "Word does not exists." );
getch( );
break;
case 3 :
show( );
getch( );
break;
case 0 :
deldic( );
exit ( 0 );
default :
printf ( "\nWrong Choice" );
}
}
}
void add ( char * str )
{
int i, j = toupper ( str [ 0 ] ) - 65;
struct node * r, * temp = dic [ j ], * q;
char mean [ 5 ] [ 20 ], ch = 'y';
i = search ( str );
if ( i )
{
printf ( "\nWord already exists." );
getch( );
return;
}
q = ( struct node * ) malloc ( sizeof ( struct node ) );
strcpy ( q -> data, str );
q -> link = NULL;
for ( i = 0; tolower ( ch ) == 'y' && i < 5; i++ )
{
fflush ( stdin );
printf ( "\n\nEnter the meaning(s) : " );
gets ( mean [ i ] );
strcpy ( q -> m [ i ] , mean [ i ] );
if ( i != 4 )
printf ( "\nAdd more meanings (y/n) " );
else
printf ( "You cannot enter more than 5 meanings." );
fflush ( stdin );
ch = getche( );
}
q -> mcount = i;
if ( dic [ j ] == NULL || strcmp ( dic [ j ] -> data, str ) > 0 )
{
r = dic [ j ];
dic [ j ] = q;
q -> link = r;
return;
}
else
{
while ( temp != NULL )
{
if ( ( strcmp ( temp -> data, str ) < 0 ) && ( ( strcmp ( temp -> link -> data, str ) > 0 ) ||
temp -> link == NULL ) )
{
q -> link = temp -> link;
temp -> link = q;
return;
}
temp = temp -> link;
}
}
}
Here is my assignment so far
#include <iostream>
#include <string>
#include <iomanip>
using namespace std;
struct subjectlist
{
string subject;
string prereq;
subjectlist *next;
};
subjectlist *start_prt=NULL;
subjectlist *current;
int option=0;
int main ()
{
int x;
string subject;
cout << "1. Add subject" << endl;
cout << "2. Search prerequisite" << endl;
cout << "3. Delete subject" << endl;
cout << "4.Show subjects" << endl;
cout << "5. Save to file" << endl;
cout << "6. Load from file" << endl;
cout << "0. Exit" << endl;
cin >> x;
switch (x)
{
case 1:
cout<<"Input subject"<<endl;
cin >> subject;
add(subject);
break;
case 2:
cout<<"Input subject to be checked"<<endl;
break;
case 3:
cout<<"Delete a subject"<<endl;
break;
case 4:
cout<<"Show Subjects"<<endl;
break;
case 5:
cout<<"Save to File"<<endl;
break;
case 6:
cout<<"Load from file"<<endl;
break;
case 0:
cout<<"exit"<<endl;
break;
default: cout <<"Invalid selection, please try again."<<endl;
}
}
void add ()
{
}

Answer 1

The add() function adds node to list. But before adding node to list, it checks whether the data in node is already present in list?
i = search ( str );
if ( i )
This checks for duplicate data.
If data is already present in list, node is not inserted in list.
If data is not present in list, it moves further.
for ( i = 0; tolower ( ch ) == 'y' && i < 5; i++ )
This for loop accepts meaning (string) in array and only 5 meanings can be added per node.
Also node is added to list in such a way that list will be in sorted form.

Answer 2

Since you are working with c++, a language, what supports object oriented programming, why not use this feature?
First you could create your data structure, what contains all the useful items, you want to store. You could also write an operator== what makes MUCH clearer to compare two Data objects:
struct Data
{
char data [20];
char m [5][20];
int mcount;
bool operator==(const Data& other)const
{
//probably you need more comparisons
return mcount==other.mcount;
}
};
Then you could create a Node class, what holds one of your Data objects, and a pointer to the next (maybe to the previous) item.
struct Node
{
Data data;
Node * next;
//Node * previous;
}
After you got this, you could just create your own linked list class:
class MyLinkedList
{
Node * head;
public:
MyLinkedList(){//initialization steps}
~MyLinkedList(){ //Delete the list}
void add(Data item)
{
if(!contains(item))
{
//append it
}
}
bool contains(Data item){ //... check if the list already contains item}
//create a string representation of the object.
//If you dont like this style, you could also provide
//an operator>> or operator<< for the class
std::string toString()
{
std::stringstream stream;
//iterate through the list, and add elements with
return stream.str();
}
};
If you got this, then in your main() it would look much clearer, what you want:
MyLinkedList list;
Data data; //somehow fill it
//adding items
list.add(data);
//printing the list
cout<<list.toString();
//after it goes out of scope the destructor will be called,
//so you dont need to bother with the deletion.