DinnerParty-class

DinnerParty.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Dinnerp
{
    class DinnerParty
    {
        const int CostOfFoodPerPerson = 25;
        private int NumberOfPeople;//人數
        public decimal CostOfBeveraagesPerPerson;//酒水的花費
        public decimal CostOfDecorations = 0;//裝修的花費


        public void SetPartyOptions(int people,bool fancy)
        {
            NumberOfPeople = people;
            CalculateCostOfDecorations(fancy);
        }

        public int GetNumberOfPeople()
        {
            return NumberOfPeople;
        }

    /// <summary>
    /// 計算酒水價格
    /// </summary>
    /// <param name="healthyOption"></param>
        public void SetHealthyOption(bool healthyOption)
        {
            if (healthyOption)
            {
                CostOfBeveraagesPerPerson = 5.00m;
            }
            else
            {
                CostOfBeveraagesPerPerson = 20.00m;
            }
            
        }
        /// <summary>
        /// 計算裝修花費
        /// </summary>
        /// <param name="fancy"></param>
        public void CalculateCostOfDecorations(bool fancy)
        {
            if (fancy)
            {
                CostOfDecorations = (this.GetNumberOfPeople() * 15m) + 50m;
            }
            else
            {
                CostOfDecorations = (this.GetNumberOfPeople() * 7.50M) + 30m;
            }
        }
      
        public decimal CalculateCost(bool healthyOption)
        {
            decimal totalCost = CostOfDecorations +
                ((CostOfBeveraagesPerPerson + CostOfFoodPerPerson) * NumberOfPeople);
            if (healthyOption)
            {
                return totalCost * .95m;
            }
            else
                return totalCost;
        }

    }
}

Form1.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Dinnerp
{
    public partial class Form1 : Form
    {
        DinnerParty dinnerParty;
        public Form1()
        {
            
            InitializeComponent();
            dinnerParty = new DinnerParty() {};
            dinnerParty.SetHealthyOption(false);
            dinnerParty.CalculateCostOfDecorations(true);
            dinnerParty.SetPartyOptions(5,true);
            DisplayDinnerPartuCost();
        }

        private void DisplayDinnerPartuCost()
        {
            decimal cost = dinnerParty.CalculateCost(checkBox2.Checked);
            costLable.Text = cost.ToString("c");
        }

        private void numericUpDown1_ValueChanged(object sender, EventArgs e)
        {
            dinnerParty.SetPartyOptions((int)peopleNumUD.Value, checkBox1.Checked);
            DisplayDinnerPartuCost();
        }

        private void checkBox1_CheckedChanged(object sender, EventArgs e)
        {
            dinnerParty.CalculateCostOfDecorations(checkBox1.Checked);
            DisplayDinnerPartuCost();
        }

        private void checkBox2_CheckedChanged(object sender, EventArgs e)
        {
            dinnerParty.SetHealthyOption(checkBox2.Checked);
            DisplayDinnerPartuCost();
        }
    }
}