foo.cc: In function 'int Mul(int, int, int*)':
foo.cc:32:12: warning: 'len' may be used uninitialized [-Wmaybe-uninitialized]
   32 |     return len;
      |            ^~~
foo.cc:23:9: note: 'len' was declared here
   23 |     int len;
      |         ^~~
foo.cc:7:13: warning: 'len' may be used uninitialized [-Wmaybe-uninitialized]
    7 |         int len;
      |             ^~~
foo.cc: In function 'int main()':
foo.cc:44:9: warning: 'len' is used uninitialized [-Wuninitialized]
   44 |     int len;
      |         ^~~

[Hydro](https://hydro.ac)提供评测服务