#include <iostream>
#include <string>
#include <vector>
#include <cctype>
#include <bitset>

using std::cin;
using std::cout;
using std::endl;
using std::string;
using std::vector;
using std::bitset;

int main()
{
    string user_bits;
    cin >> user_bits;
    const string::size_type size = user_bits.size();
    for(string::iterator iter = user_bits.begin(); iter != user_bits.end(); ++iter)
    {
        if(*iter != '0' and *iter != '1')
        {
            cout << "Only binary!" << endl;
            return -1;
        }
    }
    bitset<size> bitvec(user_bits); // <- das "size" passt ihm hier irgendwie nicht

    return 0;
}

MfG
Stromberg

Grüssli