/in/foo.cc: In function 'std::__cxx11::string gjd(std::__cxx11::string, std::__cxx11::string)':
/in/foo.cc:7:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (int i = 0; i < a.size(); i++) a1[i] = a[i] - '0';
                    ~~^~~~~~~~~~
/in/foo.cc:8:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (int i = 0; i < b.size(); i++) b1[i] = b[i] - '0';
                    ~~^~~~~~~~~~
/in/foo.cc:10:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (int i = 0; i < a.size(); i++) {
                    ~~^~~~~~~~~~
/in/foo.cc:11:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
        for (int j = 0; j < b.size(); j++) {
                        ~~^~~~~~~~~~