/in/foo.c:2:17: error: parameter 'a' has just a forward declaration
 void Output(int a[]; int size)
                 ^
/in/foo.c: In function 'Output':
/in/foo.c:6:15: error: 'a' undeclared (first use in this function)
   printf("%d",a[i]);
               ^
/in/foo.c:6:15: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c: In function 'main':
/in/foo.c:20:9: warning: passing argument 1 of 'Output' makes integer from pointer without a cast [-Wint-conversion]
  Output(a,N);
         ^
/in/foo.c:2:6: note: expected 'int' but argument is of type 'int *'
 void Output(int a[]; int size)
      ^~~~~~
/in/foo.c:20:2: error: too many arguments to function 'Output'
  Output(a,N);
  ^~~~~~
/in/foo.c:2:6: note: declared here
 void Output(int a[]; int size)
      ^~~~~~