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;
}