function+parameters.cpp

#include <iostream>
#include <string>
using namespace std;

// ===================================================
// 1. DECLARATION VS DEFINITION
// ===================================================
// Jika fungsi ditulis DI BAWAL main(), maka HARUS di-deklarasi dulu di atas.
void printMessage(); // Function Declaration (Prototype)

// Struct sederhana untuk demo Pass Structure
struct Car {
    string brand;
    int year;
};

// ===================================================
// 2. PARAMETERS & DEFAULT VALUES
// ===================================================
// Void = tidak mengembalikan nilai.
// Parameter dengan nilai default (`country = "Norway"`)
void greetUser(string fname, int age, string country = "Norway") {
    cout << "Hello " << fname << " (" << age << " y/o) from " << country << endl;
}

// ===================================================
// 3. RETURN VALUES
// ===================================================
// Fungsi dengan tipe data pengembalian (int) & kata kunci `return`
int addNumbers(int x, int y) {
    return x + y;
}

int doubleGame(int x) {
    return x * 2;
}

// ===================================================
// 4. PASS BY REFERENCE (Penting!)
// ===================================================
// Menggunakan tanda `&`. Mengubah nilai variabel ASLI di main().
void changeValue(int &num) {
    num = 50;
}

void swapNums(int &x, int &y) {
    int temp = x;
    x = y;
    y = temp;
}

// ===================================================
// 5. PASS ARRAYS & STRUCTURES TO FUNCTIONS
// ===================================================
// Menerima Array sebagai parameter
void printArray(int myNumbers[5]) {
    for (int i = 0; i < 5; i++) {
        cout << myNumbers[i] << " ";
    }
    cout << endl;
}

// Pass Structure by Reference (`&c`) agar bisa mengubah data asli & hemat memori
void updateCarYear(Car &c) {
    c.year++;
}

// ===================================================
// MAIN FUNCTION
// ===================================================
int main() {
    cout << "=== 1. CALLING FUNCTION ===" << endl;
    printMessage(); // Memanggil fungsi yang dideklarasikan di atas

    cout << "\n=== 2. PARAMETERS & DEFAULT VALUES ===" << endl;
    // "Liam" dan 20 adalah ARGUMENT
    greetUser("Liam", 20, "Indonesia"); 
    greetUser("Jenny", 14); // Menggunakan default country ("Norway")

    cout << "\n=== 3. RETURN VALUES ===" << endl;
    int result = addNumbers(5, 3);
    cout << "5 + 3 = " << result << endl;

    // Loop practical example
    for (int i = 1; i <= 3; i++) {
        cout << "Double of " << i << " is " << doubleGame(i) << endl;
    }

    cout << "\n=== 4. PASS BY REFERENCE ===" << endl;
    int val = 10;
    changeValue(val);
    cout << "Value after changeValue(): " << val << endl; // Berubah jadi 50

    int a = 10, b = 20;
    swapNums(a, b);
    cout << "After swap: a = " << a << ", b = " << b << endl;

    cout << "\n=== 5. PASS ARRAY & STRUCT ===" << endl;
    int myNums[5] = {10, 20, 30, 40, 50};
    printArray(myNums); // Cukup panggil nama array-nya saja

    Car myCar = {"Toyota", 2020};
    updateCarYear(myCar);
    cout << "Car: " << myCar.brand << ", Updated Year: " << myCar.year << endl;

    return 0;
}

// Function Definition
void printMessage() {
    cout << "I just got executed!" << endl;
}