/in/foo.cc: In member function 'BigInt BigInt::operator+(const BigInt&) const':
/in/foo.cc:25:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if (count == 0 && i >= s.size() && i >= b.s.size()) break;
                      ~~^~~~~~~~~~~
/in/foo.cc:25:41: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if (count == 0 && i >= s.size() && i >= b.s.size()) break;
                                       ~~^~~~~~~~~~~~~
/in/foo.cc:27:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if (i < s.size()) x += s[i];
        ~~^~~~~~~~~~
/in/foo.cc:28:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if (i < b.s.size()) x += b.s[i];
        ~~^~~~~~~~~~~~
/in/foo.cc: In member function 'BigInt BigInt::operator-(const BigInt&) const':
/in/foo.cc:39:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if (carry == 0 && i >= s.size() && i >= b.s.size()) break;
                      ~~^~~~~~~~~~~
/in/foo.cc:39:41: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if (carry == 0 && i >= s.size() && i >= b.s.size()) break;
                                       ~~^~~~~~~~~~~~~
/in/foo.cc:42:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if (i < s.size()) x += s[i];
        ~~^~~~~~~~~~
/in/foo.cc:44:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if (i < b.s.size()) x -= b.s[i];
        ~~^~~~~~~~~~~~
/in/foo.cc: In function 'std::ostream& operator<<(std::ostream&, const BigInt&)':
/in/foo.cc:58:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j = 0; j < strlen(buf); j++) out << buf[j];
                   ~~^~~~~~~~~~~~~