/in/foo.cc: In member function 'BigInt& BigInt::operator=(const BigInt&)':
/in/foo.cc:15:65: warning: no return statement in function returning non-void [-Wreturn-type]
     BigInt& operator = (const BigInt &other) { num = other.num; } 
                                                                 ^
/in/foo.cc: In member function 'BigInt BigInt::operator+(const BigInt&) const':
/in/foo.cc:29:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < s1.length(); i++) a[i] = s1[s1.length() - 1 - i] - '0'; 
                         ~~^~~~~~~~~~~~~
/in/foo.cc:30:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < s2.length(); i++) b[i] = s2[s2.length() - 1 - i] - '0'; 
                         ~~^~~~~~~~~~~~~
/in/foo.cc:32:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < s1.length(); i++) { 
                         ~~^~~~~~~~~~~~~
/in/foo.cc:33:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             if (i < s2.length()) 
                 ~~^~~~~~~~~~~~~