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segmentation fault at firstlist.show_list();

dereklathan (1)
any idea whats wrong? i'm stumped.


#ifndef LISTS_H
#define LISTS_H

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

class Lists {
int A;

private:
struct Node{
int number;
Node *link;
};
typedef Node* NodePtr;
NodePtr head;

public:
void head_insert(NodePtr&, int);
Lists();
void add(int);
void merge_lists(NodePtr, NodePtr);
void show_list();
};
#endif

#include <iostream>
#include <cstddef>
#include <cstring>
#include "lists.h"
using namespace std;

Lists::Lists(){
NodePtr head;
head = new Node;
head = NULL;}

void Lists::head_insert(NodePtr& head, int a_number)
{
NodePtr temp_ptr;
temp_ptr = new Node;

temp_ptr-> number = a_number;

temp_ptr->link = head;
head = temp_ptr;
delete temp_ptr;
}

void Lists::show_list()
{
NodePtr here;
here = head;

while (here != NULL)
{
cout << here-> number << endl;
here = here->link;
}
}




void Lists::add(int the_number){
NodePtr temp_head;
if(head==NULL){
head->number=the_number;
head->link=NULL;
}
else
head_insert(head, the_number);

}

#include <iostream>
#include <cstddef>
#include "lists.h"
using namespace std;


int main(){
int listsize;
Lists firstlist;
Lists secondlist;
Lists mergedlist;
cout << "how many integers for the first list?\n";
cin >> listsize;
int list1[listsize];
cout << "enter " << listsize << " integers in numerical order.\n";
for(int i=0;i<listsize;i++)
cin >> list1[i];
for(int i=0;i<listsize;i++)
firstlist.Lists::add (list1[i]);
cout << "how many for the second?\n";
cin >> listsize;
int list2[listsize];
cout << "enter " << listsize << " integers in numerical order.\n";
for(int i=0;i<listsize;i++)
cin >> list2[i];
for(int i=0;i<listsize;i++)
secondlist.add (list2[i]);
firstlist.show_list();
return 0;
}
moorecm (1932)
Here's a couple ideas:
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#ifndef LISTS_H
#define LISTS_H

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

class Lists {                                                               // why plural?
int A;

private:
struct Node{
int number;
Node *link;
};
typedef Node* NodePtr;
NodePtr head;

public:
void head_insert(NodePtr&, int);
Lists();
void add(int);
void merge_lists(NodePtr, NodePtr);
void show_list();
};
#endif

#include <iostream>
#include <cstddef>
#include <cstring>
#include "lists.h"
using namespace std;

Lists::Lists(){
NodePtr head;
head = new Node;
head = NULL;}

void Lists::head_insert(NodePtr& head, int a_number)
{
NodePtr temp_ptr;
temp_ptr = new Node;

temp_ptr-> number = a_number;

temp_ptr->link = head;
head = temp_ptr;
delete temp_ptr;
}

void Lists::show_list()
{
NodePtr here;
here = head;

while (here != NULL)
{
cout << here-> number << endl;
here = here->link;
}
}




void Lists::add(int the_number){
NodePtr temp_head;
                                                                            // I'd rethink this logic:
if(head==NULL){
head->number=the_number;                                                    // error!  head is null, you can't call its member!
head->link=NULL;
}
else
head_insert(head, the_number);

}

#include <iostream>
#include <cstddef>
#include "lists.h"
using namespace std;


int main(){
int listsize;
Lists firstlist;
Lists secondlist;
Lists mergedlist;
cout << "how many integers for the first list?\n";
cin >> listsize;
int list1[listsize];                                                        // this is nonstandard, I'm guessing you use GCC
cout << "enter " << listsize << " integers in numerical order.\n";
for(int i=0;i<listsize;i++)
cin >> list1[i];
for(int i=0;i<listsize;i++)
firstlist.Lists::add (list1[i]);                                            // why not do this in the last loop?
cout << "how many for the second?\n";
                                                                            // etc.
cin >> listsize;
int list2[listsize];
cout << "enter " << listsize << " integers in numerical order.\n";
for(int i=0;i<listsize;i++)
cin >> list2[i];
for(int i=0;i<listsize;i++)
secondlist.add (list2[i]);
firstlist.show_list();
return 0;
}
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