foo.cc: In function 'void Concat(char*, char*)':
foo.cc:6:23: warning: unused variable 'm' [-Wunused-variable]
    6 |         int i, n = 0, m = 0, k = 0,j;
      |                       ^
foo.cc:6:30: warning: unused variable 'k' [-Wunused-variable]
    6 |         int i, n = 0, m = 0, k = 0,j;
      |                              ^
foo.cc:6:36: warning: unused variable 'j' [-Wunused-variable]
    6 |         int i, n = 0, m = 0, k = 0,j;
      |                                    ^

[Hydro](https://hydro.ac)提供评测服务