// sayhi.h
#ifndef SAYHI_H_
#define SAYHI_H_

void sayhi(char*);

#endif


// sayhi.c
#include "sayhi.h"
#include <stdio.h>

void sayhi(char* szName) {
    printf("Hi there, %s\n", szName);
}


// main.c
#include "sayhi.h"

int main(int argc, char** argv) {
    sayhi("Mike");
    return 0;
}