Compilare: user.cpp: In member function 'BigInt& BigInt::operator+=(const BigInt&)': user.cpp:41: warning: comparison between signed and unsigned integer expressions user.cpp:40: warning: unused variable 'i' user.cpp:51: warning: comparison between signed and unsigned integer expressions user.cpp:50: warning: unused variable 'x' user.cpp: In member function 'BigInt& BigInt::operator+=(long long int)': user.cpp:71: warning: comparison between signed and unsigned integer expressions