#include <iostream>
#include <fstream>
#include <string>
using namespace std;
 
//Declares functions
int calc(string a);
void valid(int a, string b, ofstream & c);
 
//main function
int main () {
 
	char isbn;
	int total;
 
	//declares the output and input file
	ofstream outfile ("program1.out");
	ifstream myfile ("isbn.dat");
	//stops the program if the file's not found
	if(!myfile){
		cout<<"File not found.\n";
		exit(1);
	}
 
	//Declares string
	string line;
 
	//Reads contents of file till it ends
	while(myfile>>line){ 
		cout<<line<<'\t';
		//calculates total and stores it
		total = calc(line);
		//checks if ISBN is valid and stores in output file
 
 
			cout<<"\t invaild \n";
 
			//Writes to output file
			outfile<<line<<"\t invalid \n";
		}
		else
			valid(total, line, outfile);
 
	}
 
	return 0;
}
 
int calc (string a) {
 
	int i;
	int j;
	int total;
	int value;
	int store[10];
 
	//runs until the string ends
	for(i=0; i < a.length(); i++){
		//erases the "-" from the string
 
		if (a[i] == '-') {
			a.erase(i, 1);
			i--;
		}
	}
 
		for(i=0; i < a.length(); i++){
		//converts a char to an int
		value = a[i] - '0';
		store[i] = value;
 
	}
 
		total = (1*store[0] + 2*store[1] + 3*store[2] + 4*store[3] + 5*store[4] + 6*store[5] + 7*store[6] + 8*store[7] + 9*store[8]) % 11;
	//calculates total
		return total;
}
 
//checks the valididty of said ISBN number
void valid(int a, string b, ofstream & c){
 
	//if int total is = to the last number in the ISBN then print valid
	if (a == b[b.length() -1]) {
		cout<<"\t valid \n";
		//Writes to output file
		c<<b<<"\t valid \n";
	}
	//if total if a is = 10 and the last number is "x" then print valid
	else if (a == 10 && b[b.length() -1] == 'x') {
		cout<<"\t valid \n";
		//Writes to output file
		c<<b<<"\t valid \n";
	}
	//anything else print invalid
	else {
		cout<<"\t invaild \n";
		//Writes to output file
		c<<b<<"\t invalid \n";
	}
}

0-13-018661-9
0-13-096141-8
0-201-88336-8
0-534-91504-x
0-88185-020-4

		for(i=0; i < a.length(); i++){
		//converts a char to an int
		value = a[i] - '0';
		store[i] = value;

		for(i=0; i <= a.length(); i++){
		//converts a char to an int
		value = a[i] - '0';
		store[i] = value;