In file included from main.cpp:8:0:
num.cpp:13:5: error: prototype for 'Num Num::operator+=(const Num&)' does not match any in class 'Num'
 Num Num::operator+=(const Num& other) {
     ^~~
In file included from main.cpp:7:0:
num.h:19:10: error: candidates are: Num& Num::operator+=(int)
     Num& operator+=(int num);
          ^~~~~~~~
num.h:16:10: error:                 Num& Num::operator+=(const Num&)
     Num& operator+=(const Num& other);    
          ^~~~~~~~