/in/foo.c: In function 'Gcd':
/in/foo.c:9:20: warning: 'return' with a value, in function returning void
  if(n == 0) return m;
                    ^
/in/foo.c:2:6: note: declared here
 void Gcd(int m,int n)/*最大公约数*/
      ^~~
/in/foo.c: At top level:
/in/foo.c:12:6: warning: return type of 'main' is not 'int' [-Wmain]
 void main()
      ^~~~
/in/foo.c: In function 'main':
/in/foo.c:16:5: error: void value not ignored as it ought to be
  gys=Gcd(A,B);
     ^