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 商城收银软件
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        double total = 0.0d;//声明一个double变量,用total来计算总计
        private void button1_Click(object sender, EventArgs e)
        {
            double totalPrices = Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text);
total = total + totalPrices;//将每个商品合计计算出来
lbxList.Text = "单价:" + txtPrice.Text + "数量:" + txtNum.Text + "合计:" + totalPrices.ToString();  //显示信息
            lblResult.Text = total.ToString();//显示总计数
         }
     }
}

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 商城收银软件
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        double total = 0.0d;//声明一个double变量,用total来计算总计
        private void button1_Click(object sender, EventArgs e)
        {
            double totalPrices = 0d;
            switch (cbxType.SelectedIndex)
            {
                case 0:
                    totalPrices = Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text);
                    break;
                case 1:
                    totalPrices = Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text)*0.8;
                    break;
                case 2:
                    totalPrices = Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text)*0.7;
                    break;
                case 3:
                    totalPrices = Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text)*0.5;
                    break;
            }
            total = total + totalPrices;
            lbxList.Text = "单价:" + txtPrice.Text + "数量:" + txtNum.Text + " " + cbxType.SelectedItem + "合计:" + totalPrices.ToString();  
            lblResult.Text = total.ToString();


        }
        private void Form1_Load(object sender, EventArgs e)
        {
            cbxType.Items.AddRange(new object[] { "正常收费", "打八折", "打七折", "打五折" });
            cbxType.SelectedIndex = 0;
        }
}