/* isbn.cpp
 * Write a program to check if a number entered by the user is a 
 * valid ISBN number.
 * 
 * Go to http://www.cs.queensu.ca/home/bradbury/checkdigit/isbncheck.htm
 * for info on ISBN numbers.
 */ 

#include <iostream>
#include <cstring>

using namespace std;

const int ISBNSIZE = 13; 

bool isValid(const char *isbn);
void copyNoHyphen(const char *isbn, char *copy);

int main(int argc, char *argv[])
{      
    char isbn [ISBNSIZE + 1];
    cout << "Enter ISBN number" << endl;
    cin >> isbn;
    if(isValid(isbn)){
        cout << "Yep, its a valid number" <<endl;
    }else{
        cout << "Sorry, Not a valid number" <<endl;
    }    
    system("PAUSE");
    return EXIT_SUCCESS;
}
bool isValid(const char *isbn){   
    const char ZERO = '0';
    const int COPYSIZE = 10;       
    char copy[COPYSIZE + 1];
    
    copyNoHyphen(isbn,copy); 
    if(strlen(copy) != 10){
        cout << "Less than 10  " << strlen(copy)<< endl;
        return false;
    }  
                
    int sum = copy[0] - ZERO;             
    for(int i = 1; i < (COPYSIZE - 1); ++i){   
        int temp = copy[i] - ZERO;        
        sum += temp * (i + 1);       
    }  
        
    int remainder = sum % 11;   
    if(remainder == 10) {
        if(copy[COPYSIZE - 1] == 'X') {
            return true;
        }else{
            return false;
        }
    }
    else if(remainder != (copy[COPYSIZE -1] - ZERO)){
        return false;
    }      
    return true;
}

void copyNoHyphen(const char *isbn, char *copy){ 
    const char HYPHEN = '-'; 
    int j = 0;     
    for(int i = 0; i < ISBNSIZE; ++i){
        if(*(isbn + i ) != HYPHEN){  
            *(copy + j++) = *(isbn + i);            
        }               
    } 
    *(copy + j) = '\0';    
}