计算器

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

namespace partice04
{
    /// <summary>
    /// 父类
    /// </summary>
    public class Operation
    {
        /// <summary>
        /// 分别2个数字
        /// </summary>
        public double NumA { get; set; }
        public double NumB { get; set; }

        /// <summary>
        /// 虚方法
        /// </summary>
        /// <returns></returns>
        public virtual double GetResult()
        {
            double result = 0;
            return result;
        }

    }
}

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

namespace partice04
{
    /// <summary>
    /// 加法类
    /// </summary>
    public class Operation_Add:Operation
    {
        /// <summary>
        /// 重写父类GetResult()方法
        /// </summary>
        /// <returns></returns>
        public override double GetResult()
        {
            double result = NumA + NumB;
            return result;
        }
    }
}

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

namespace partice04
{
    /// <summary>
    /// 减法类
    /// </summary>
    public class Operation_Minus : Operation
    {
        /// <summary>
        /// 重写父类GetResult()方法
        /// </summary>
        /// <returns></returns>
        public override double GetResult()
        {
            double result = NumA - NumB;
            return result;
        }
    }
}

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

namespace partice04
{
    /// <summary>
    /// 乘法类
    /// </summary>
    public class Operation_Multiply:Operation
    {
        /// <summary>
        /// 重写父类GetResult()方法
        /// </summary>
        /// <returns></returns>
        public override double GetResult()
        {
            double result = NumA * NumB;
            return result;
        }
    }
}

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

namespace partice04
{
    /// <summary>
    /// 除法类
    /// </summary>
    public class Operation_Divide:Operation
    {
        /// <summary>
        /// 重写父类GetResult()方法
        /// </summary>
        /// <returns></returns>
        public override double GetResult()
        {
            //判断数字是否为0
            if (NumB == 0)
            {
                throw new Exception("除数不能为0！");
            }
            double result = NumA / NumB;
            return result;
        }
    }
}

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 partice04
{
    public partial class FrmMain : Form
    {
        public FrmMain()
        {
            InitializeComponent();
            BindOperation();
        }

        /// <summary>
        /// 设定运算符号
        /// </summary>
        public void BindOperation()
        {
            this.cbmCount.Items.Clear();
            this.cbmCount.Items.Add("请选择");
            this.cbmCount.Items.Add("＋");
            this.cbmCount.Items.Add("－");
            this.cbmCount.Items.Add("×");
            this.cbmCount.Items.Add("÷");
        }

        /// <summary>
        /// 点击计算按钮
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnCalcu_Click(object sender, EventArgs e)
        {
            //判断文本框是否为空
            if (string.IsNullOrEmpty(txtNum1.Text.Trim()) || string.IsNullOrEmpty(txtNum2.Text.Trim()))
            {
                MessageBox.Show("操作数不能为空！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Error);
                txtNum1.Focus();
                return;
            }
            try
            {
                Operation opr = new Operation();
                //switch功能，调用不同的方法
                switch (cbmCount.Text.Trim())
                {
                    case "＋":
                        opr = new Operation_Add();
                        break;
                    case "－":
                        opr = new Operation_Minus();
                        break;
                    case "×":
                        opr = new Operation_Multiply();
                        break;
                    case "÷":
                        opr = new Operation_Divide();
                        break;
                    case "请选择":
                        MessageBox.Show("请选择运算符号！");
                        break;
                }
                opr.NumA = double.Parse(txtNum1.Text.Trim());
                opr.NumB = double.Parse(txtNum2.Text.Trim());

                lblResult.Text = opr.GetResult().ToString();

            }
            catch (Exception ex)
            {
                MessageBox.Show("发生错误！" + ex.Message);
            }
        }
    }
}

窗体布局图：

效果视频：

　　请移步至 --> http://www.bilibili.com/video/av9753359/