UVA_333_Recognizing Good ISBNs

#include<iostream>    
#include<sstream>    
#include<string>    
#include<vector>    
#include<list>    
#include<set>    
#include<map>    
#include<stack>    
#include<queue>    
#include<algorithm>  
#include<bitset>
#pragma warning(disable:4996)    
using std::cin;
using std::cout;
using std::endl;
using std::stringstream;
using std::string;
using std::vector;
using std::list;
using std::pair;
using std::set;
using std::multiset;
using std::map;
using std::multimap;
using std::stack;
using std::queue;
using std::priority_queue;
using std::bitset;
bool check(const string &ISBN)
{
	vector<int>digit;
	for (size_t i = 0; i < ISBN.size(); i++)
	{
		if (isdigit(ISBN[i]))
		{
			digit.push_back(ISBN[i] - '0');
		}
		else if (ISBN[i] == 'X')
		{
			digit.push_back(10);
			if (digit.size() != 10)
			{
				return false;
			}
		}
	}
	if (digit.size() != 10)
	{
		return false;
	}
	for (size_t i = 1; i < digit.size(); i++)
	{
		digit[i] += digit[i - 1];
	}
	for (size_t i = 1; i < digit.size(); i++)
	{
		digit[i] += digit[i - 1];
	}
	if (digit.size()==10&& digit[9] % 11 == 0)
	{
		return true;
	}
	return false;
}
string clear_space(const string &str)
{
	string ret=str;
	while (ret[0] == ' ')
	{
		ret.assign(ret.begin() + 1, ret.end());
	}
	while (ret[ret.size() - 1] == ' ')
	{
		ret.pop_back();
	}
	return ret;
}
int main()
{
	//freopen("input.txt", "r", stdin);    
	//freopen("output.txt", "w", stdout);
	string ISBN;
	while (getline(cin,ISBN))
	{
		if (!ISBN.size())
		{
			cout << " is incorrect." << endl;
			continue;
		}
		ISBN = clear_space(ISBN);
		cout << ISBN;
		if (check(ISBN))
		{
			cout << " is correct."<<endl;
		}
		else
		{
			cout << " is incorrect." << endl;
		}
	}
	return 0;
}