menu.cpp

#include<iostream>
#include<cstdlib> //stdlib.h
using namespace std; //cout,cin,endl -> std::
float calculateArea(float l, float w); //fun declare
int calculateGoldPrice(int kyat, int pae, int yway, int currentGoldPrice);
int main()
{
    int ans = 0;
    while (ans != 3)
    {
        system("cls");
        cout << "Menu System" << endl;
        cout << "    1-Calculate Area" << endl;
        cout << "    2-Calculate Gold Price" << endl;
        cout << "    3-Exit" << endl;
        cout << "    Choose 1,2,3: ";
        cin >> ans;

        if (ans == 1) {
            cout << "Area calculation" << endl;
            calculateArea(11, 22);
        }
        else if (ans == 2)
        {
            cout << "Gold price calculation" << endl;
            calculateGoldPrice(1, 2, 3, 6000000);
        }
        else if (ans == 3) {
            cout << "Bye" << endl;
            exit(0);
        }
        else {
            cout << "Invalid input, choose 1,2,3 only!" << endl;
        }
        system("pause");
    }
    return 0;
}

float calculateArea(float l, float w) //fun definition
{
    float a = 0.0F;
    a = l * w;
    return a;
}

int calculateGoldPrice(int kyat, int pae, int yway, int currentGoldPrice)
{
    int totalGoldPrice = 0.0;
    //calculate it
    return totalGoldPrice;
}