foo.c: In function ‘main’:
foo.c:6:9: warning: implicit declaration of function ‘input’ [-Wimplicit-function-declaration]
    6 |         input(a, n);
      |         ^~~~~
foo.c:7:9: warning: implicit declaration of function ‘func’ [-Wimplicit-function-declaration]
    7 |         func(a, n);
      |         ^~~~
foo.c: In function ‘input’:
foo.c:18:1: warning: control reaches end of non-void function [-Wreturn-type]
   18 | }
      | ^
foo.c: In function ‘func’:
foo.c:36:1: warning: control reaches end of non-void function [-Wreturn-type]
   36 | }
      | ^