/in/foo.c: In function 'main':
/in/foo.c:6:2: warning: implicit declaration of function 'input' [-Wimplicit-function-declaration]
  input(a, n);
  ^~~~~
/in/foo.c:7:14: warning: implicit declaration of function 'func' [-Wimplicit-function-declaration]
  printf("%d",func(a, n));
              ^~~~
/in/foo.c: In function 'input':
/in/foo.c:18:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^