foo.cc: In function 'int lcm(int, int)':
foo.cc:31:6: warning: unused variable 'lcm' [-Wunused-variable]
  int lcm=a/gcd(a,b)*b;
      ^~~
foo.cc:32:2: warning: no return statement in function returning non-void [-Wreturn-type]
  }
  ^
foo.cc: In function 'int main()':
foo.cc:8:9: warning: 'n' is used uninitialized in this function [-Wuninitialized]
  int a[n];
         ^

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。