In file included from main.cpp:8:0:
num.cpp: In member function 'Num& Num::operator+=(const Num&)':
num.cpp:35:1: error: no return statement in function returning non-void [-Werror=return-type]
 }
 ^
num.cpp: In member function 'Num& Num::operator-=(const Num&)':
num.cpp:45:1: error: no return statement in function returning non-void [-Werror=return-type]
 }
 ^
num.cpp: In member function 'Num& Num::operator*=(const Num&)':
num.cpp:49:1: error: no return statement in function returning non-void [-Werror=return-type]
 }
 ^
num.cpp: In member function 'Num& Num::operator+=(int)':
num.cpp:53:1: error: no return statement in function returning non-void [-Werror=return-type]
 }
 ^
num.cpp: In member function 'Num& Num::operator-=(int)':
num.cpp:63:1: error: no return statement in function returning non-void [-Werror=return-type]
 }
 ^
num.cpp: In member function 'Num& Num::operator*=(int)':
num.cpp:67:1: error: no return statement in function returning non-void [-Werror=return-type]
 }
 ^
cc1plus: all warnings being treated as errors