/in/foo.c: In function 'main':
/in/foo.c:9:2: warning: implicit declaration of function 'Output' [-Wimplicit-function-declaration]
  Output(a,n);
  ^~~~~~
/in/foo.c: At top level:
/in/foo.c:12:6: warning: conflicting types for 'Output'
 void Output(int a[], int n)
      ^~~~~~
/in/foo.c:9:2: note: previous implicit declaration of 'Output' was here
  Output(a,n);
  ^~~~~~