/in/foo.c: In function 'main':
/in/foo.c:8:2: warning: implicit declaration of function 'OutPut' [-Wimplicit-function-declaration]
  OutPut(n);
  ^~~~~~
/in/foo.c: At top level:
/in/foo.c:11:6: warning: conflicting types for 'OutPut'
 void OutPut(int n) {
      ^~~~~~
/in/foo.c:8:2: note: previous implicit declaration of 'OutPut' was here
  OutPut(n);
  ^~~~~~