#include <iostream>
#include <cassert>

using namespace std;

const char* BINARY_DIGITS = "01";

int bin2int(const char* txt);
int binaryDigitValue(char digit); // Return 0, 1, or -1 for
                                  // non-binary digit
int main() {
    char txt[64];
    while (true) {
        cout << "Enter a binary representation of an integer number"
                " (q for the end):" << endl;
        if (!(cin.getline(txt, 62)) || txt[0] == 'q')
            break;
        int n = bin2int(txt);
        cout << "Integer: " << n << endl;
    }
    return 0;
}

int bin2int(const char* txt) {
    int s = 1;          // Sign of a number
    if (*txt == '-') {
        s = (-1);
        ++txt;
    }
    int n = 0;
    while (*txt != 0) {
        int d = binaryDigitValue(*txt);
        if (d < 0)
            break;
        n = n*2 + d;
        ++txt;
    }
    return s*n;
}

int binaryDigitValue(char digit) {
    int d = 0;
    while (d < 2) {
        if (digit == BINARY_DIGITS[d])
            return d;
        ++d;
    }
    return (-1); // This is not a binary digit
}