compiles but wont run

//////////////////////Main Program///////////////////////////////////////////////

#include <iostream>
#include <fstream>
#include <cstring>
#include "ISBN.h"
#include "Book.h"
using namespace std;

const int NUMBER_OF_BOOKS = 15;

void check_isbn_class();
void check_book_class();

int main() {
check_isbn_class();
check_book_class();
return 0;
}

void check_isbn_class() {
char isbns[13][14];
int index=0;
strcpy(isbns[index++], "1-57676-074-X");
strcpy(isbns[index++], "0-12-597121-2"); // correct check digit is 4
strcpy(isbns[index++], "0-385-49532-3");
strcpy(isbns[index++], "0-321-19724-X"); // correct check digit is 0
strcpy(isbns[index++], "0-02-360692-4");
strcpy(isbns[index++], "0-321-19362-5"); // correct check digit is 8
strcpy(isbns[index++], "0-201-70433-1");
strcpy(isbns[index++], "1-56592-324-2"); // correct check digit is 3
strcpy(isbns[index++], "0-321-19498-5");
strcpy(isbns[index++], "0-13-034074-9"); // correct check digit is X
strcpy(isbns[index++], "0-13-790395-2");
strcpy(isbns[index++], "0-471-46983-0"); // correct check digit is 1
strcpy(isbns[index++], "0-670-82162-4");

for (int i=0; i<13; i++) {
ISBN isbn(isbns[i]);
isbn.print(cout);
if (isbn.valid())
cout << " is valid\n";
else cout << " is not valid\n";
}

ISBN isbn1("0", "670", "82162"),
isbn2("0", "13", "034074");
isbn1.print(cout); // should print "0-670-82162-4"
cout << endl;
isbn2.print(cout); // should print "0-13-034074-X"
cout << endl;
}

void check_book_class() {
Book texts[NUMBER_OF_BOOKS];
char title[81], author[81], isbn[14];
char publisher[8];
ifstream infile;
infile.open( "books.txt" );
if (!infile) {
cout << "Unable to open file books.txt\n";
return;
}
for (int i=0; i<NUMBER_OF_BOOKS; i++) {
infile.getline(title, 81);
cout << title << endl;
infile.getline(author, 81);
infile.getline(isbn, 14);
Book thisbook(title, author, isbn);
cout << "just read this book:\n";
thisbook.print(cout);
cout << endl;
texts[i] = thisbook;
}
cout << "Here are all of the books in the database\n\n";
for (int i=0; i<NUMBER_OF_BOOKS; i++) {
texts[i].print(cout);
cout << endl;
}
while (true) {
cout << "Enter a publisher code, or 'quit' to stop\n";
cin >> publisher;
if (strcmp(publisher, "quit") == 0) return;
cout << "Books by this publisher:\n\n";
for (int i=0; i<NUMBER_OF_BOOKS; i++)
if (strcmp(texts[i].getpublisher(), publisher) == 0) {
texts[i].print(cout);
cout << endl;
}
}
}

////////////////ISBN Class/////////////////////////////////////////////////////////

#include<iostream>
using namespace std;

class ISBN
{
public:
ISBN();
ISBN(char[ ]); // e.g., ISBN book("0-670-82162-4");
ISBN(char[ ], char[ ], char[ ], char); // 4-argument constructor is passed
// group code, publisher code, book
// code, and check character. e.g.
// ISBN book("0","670","82162","4");
ISBN(char[ ], char[ ], char[ ]); // 3-argument constructor is passed
// group code, publisher code, and
// book code. It computes the
// check character
// e.g. ISBN book("0","670","82162");
bool valid(); // true if check character is correct
char *getpublisher(); // return publisher code
void print(ostream &o); // print string with hyphens
int char_to_int(char c);

private:
char group[6]; // group code is 1-5 digits
char publisher[8]; // publisher code is 1-7 digits
char book[8]; // book code is 1-7 digits
char check;

int concat2[20];
char compute_check(); // compute the check character

};



ISBN::ISBN(char a[], char b[], char c[], char d)
{
strcpy(group, a);
strcpy(publisher, b);
strcpy(book, c);
check = d;
}

ISBN::ISBN(char a[], char b[], char c[])
{
strcpy(group, a);
strcpy(publisher, b);
strcpy(book, c);
check = compute_check();
}

ISBN::ISBN(char a[])
{
char deliminator[] = "-";
char check2[2];
strtok(a, deliminator);
strcpy(group, a);
strtok(NULL, deliminator);
strcpy(publisher, NULL);
strtok(NULL, deliminator);
strcpy(book, NULL);
strtok(NULL, deliminator);
strcpy(check2, NULL);
check = check2[0];
}

ISBN::ISBN(){}

char ISBN::compute_check()
{
char concat1[20];
strcat(concat1, group);
strcat(concat1, publisher);
strcat(concat1, book);
for (int i = 0; i <= 9; i++)
{
concat2[i] = char_to_int(concat1[i]);
}
int checkNumber = (concat2[0] * 1) + (concat2[1] * 2) + (concat2[2] * 3) + (concat2[3] * 4) + (concat2[4] * 5) + (concat2[5] * 6) + (concat2[6] * 7) + (concat2[7] * 8) + (concat2[8] * 9);
checkNumber = checkNumber % 11;
char checkChar = checkNumber;
if (checkNumber = 10)
checkChar = 'X';
return checkChar;
}

bool ISBN::valid()
{
char checkTest = compute_check();
return (checkTest = check);
}

char * ISBN::getpublisher()
{
return publisher;
}

void ISBN::print(ostream &o)
{
cout<<group<<"-"<<publisher<<"-"<<book<<"-"<<check<<endl;
}

//Function used to convert chars to int.

int ISBN::char_to_int(char c)
{
return c - '0';
}

///////////////////////BOOK CLASS///////////////////////////////////
#include <iostream>
#include "ISBN.h"
using namespace std;

class Book {
private:
char title[81]; // title no more than 80 characters
char author[51]; // author no more than 50 characters
ISBN isbn; // the book's ISBN

public:
Book();
Book(char[ ], char[ ], char[ ]); // e.g., ISBN book("The Odyssey",

// "Homer", "0-670-82162-4");
char *gettitle();
char *getauthor();
ISBN getisbn();
char *getpublisher(); // look up the publisher code
// in the isbn
void print(ostream &o); // print title, author, and isbn
};

Book::Book(char a[ ], char b[ ], char c[ ])
{
strcpy(title, a);
strcpy(author, b);
ISBN isbn(c);

}

Book::Book(){}

char * Book::gettitle()
{return title;}

char * Book::getauthor()
{return author;}

ISBN Book::getisbn()
{return isbn;}

char * Book::getpublisher()
{
return isbn.getpublisher();
}

void Book::print (ostream &o)
{
cout<<title<<", "<<author<<", "<<endl;
isbn.print(cout);
}

There ya go dude
http://www.agilman.org/crap/problem.cpp

I didn't solve it, but Im narrowing it down for ya

When you run main, it calls check_isbn_class()...
check_isbn_class runs a loop where it constantly generates objects type ISBN.
THe problem is somewhere in your ISBN class. Im about to start narrowing it down, tho Im kinda tired.

(ohh, and notice the indent style, makes code more readable)

Hope that helps ya.

...or you could try a "new" way - run it under debugger.
You'll see that the crush is here:strcpy(publisher, NULL);