/in/foo.cc: In member function 'BigNum BigNum::operator+(const BigNum&) const':
/in/foo.cc:51:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if(g == 0 && i >= a.size() && i >= b.a.size()) break;
                 ~~^~~~~~~~~~~
/in/foo.cc:51:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if(g == 0 && i >= a.size() && i >= b.a.size()) break;
                                  ~~^~~~~~~~~~~~~
/in/foo.cc:53:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if(i < a.size()) x += a[i];
       ~~^~~~~~~~~~
/in/foo.cc:54:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if(i < b.a.size()) x += b.a[i];
       ~~^~~~~~~~~~~~
/in/foo.cc: In member function 'BigNum BigNum::operator-(const BigNum&) const':
/in/foo.cc:67:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if(i >= A.a.size() && i >= B.a.size()) break;
       ~~^~~~~~~~~~~~~
/in/foo.cc:67:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if(i >= A.a.size() && i >= B.a.size()) break;
                          ~~^~~~~~~~~~~~~
/in/foo.cc:68:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if(i >= B.a.size()) C.a[i] = A.a[i];
       ~~^~~~~~~~~~~~~
/in/foo.cc:72:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if(i >= C.a.size()) break;
       ~~^~~~~~~~~~~~~
/in/foo.cc: In member function 'BigNum BigNum::operator*(const BigNum&) const':
/in/foo.cc:84:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i = 0; i < a.size(); i++){
                  ~~^~~~~~~~~~
/in/foo.cc:86:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j = 0; j < b.a.size(); j++){
                   ~~^~~~~~~~~~~~