incomplete type not allowed, function dec/def and no classes

Question

So i keep getting an "incomplete type not allowed error" on the emphasized call of function "out" on this and ive switched the function decs around, and i decided to not move on until i have this figured out because i can't find any non-class examples that aren't completely analogically opaque. Noob question but any help would be appreciated.

its supposed to be a simple fibonacci function but obviously i haven't written all the code. Cpp 14 ( on g++, im getting syntax highlights suggesting its 11, however).

#include <string>
#include <iostream> 

int fib(int x);
int input();
void out(int p);

int fib(int x) {
    // int* prim;
    // int* sec;
    // *prim = 1;
    // *sec = 1;
    // int count = 

}

int main(){

    void out( fib( input() ) );  // error here // out on this line
    return 0;
}

int input (){
    int inp = 0;
    
}

void out(int p){
    std::cout << "the number is: " << p ;
}

Answer 1

This:

 int main(){
      void out( fib( input() ) );  // error here
 }

is interpreted to something like an instantiation of a variable of type void calling the constructor that accepts a int as first parameter, instead you probably want this:

   int main(){
       out( fib( input() ) );  
   } 

that is just a function call