foo.cc: In function 'int main()':
foo.cc:6:8: warning: unused variable 'n' [-Wunused-variable]
    6 |  int i,n,w,num=0;
      |        ^
foo.cc:6:10: warning: unused variable 'w' [-Wunused-variable]
    6 |  int i,n,w,num=0;
      |          ^
foo.cc:6:12: warning: unused variable 'num' [-Wunused-variable]
    6 |  int i,n,w,num=0;
      |            ^~~

[Hydro](https://hydro.ac)提供评测服务