Compilare: user.cpp: In member function ‘void big_int::add(big_int)’: user.cpp:44: warning: comparison between signed and unsigned integer expressions user.cpp: In member function ‘big_int big_int::multiply(long long int)’: user.cpp:105: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘int main()’: user.cpp:133: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result