Tệp header và tệp nguồn

#ifndef HELPERS_H
#define HELPERS_H

#include <string>

std::string greet(std::string name);
int addNumbers(int a, int b);

#endif

#include "helpers.h"

std::string greet(std::string name) {
    return "Hello, " + name + "!";
}

int addNumbers(int a, int b) {
    return a + b;
}

#include <iostream>
#include "helpers.h"

int main() {
    std::cout << greet("Alice") << std::endl;
    std::cout << addNumbers(5, 3) << std::endl;
    return 0;
}

Hello, Alice!
8