freepoulite

Since a few days, I'm learning how to build external in C

but i can't figure out how can i use the inlet 0 ( default)

void simplemax_in0(t_simplemax *x,long n); //prototype

void simplemax_in0(t_simplemax *x,long n){

but the inlet 0 don't understand int ( max window message)

Since a few days, I'm learning how to build external in C
but i can't figure out how can i use the inlet 0 ( default)
I've tried to add 

void simplemax_in0(t_simplemax *x,long n){
    post("hello world! );
}

use the default inlet of an external