greet.c

// This file implements the interface described in its header (greet.h)

#include "greet.h"
#include <stdio.h>

void greet(char* name) {
  printf("Hello, %s!\n", name);
}

greet.h

// This file describes the public interface greet.c should implement
// In this case, a single function, greet()

#pragma once // Ensures header is only included once by the compiler

void greet(char* name);

hello.c

// This file is our entry-point

#include "greet.h" // Include the header so we can call greet()

int main(void) {
  greet("World");
  return 0;
}