C#四则运算之策略模式

Calculator.cs

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

namespace stratage
{
    public abstract class Calculator    //抽象类 Calculator
    {
        public abstract double Cal(double a, double b); //抽象方法Cal
    }
    public class Add : Calculator      //派生类Add继承抽象类Calculator
    {
        public override double Cal(double a, double b)//并重写了抽象方法Cal
        {
            double result = 0;
            result = a + b;
            return result;
        }
    }
    public class Sub : Calculator
    {
        public override double Cal(double a, double b)
        {
            double result = 0;
            result = a - b;
            return result;
        }
    }
    public class Mul : Calculator
    {
        public override double Cal(double a, double b)
        {
            double result = 0;
            result = a * b;
            return result;
        }
    }
    public class Div : Calculator
    {
        public override double Cal(double a, double b)
        {
            double result = 0;
            result = a / b;
            return result;
        }
    }
    public class Context           //上下文
    {
        private Calculator calculate = null;//实例化一个基类的引用对象
        public Context(Calculator _cal)//_cal为派生类的一个对象
        {
            this.calculate = _cal;    //把派生类的对象赋给基类的引用对象
        }
        public double Cal(double a, double b, String symbol)
        {
            return this.calculate.Cal(a, b);//返回计算结果
        }
    }
}

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.Windows.Forms;
using System.IO;

namespace stratage
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        int Count=0;
        int Right=0;
        public static String AddSymbol = "+";  //加法
        public static String SubSymbol = "-";  //减法
        public static String MulSymbol = "*";  //乘法
        public static String DivSymbol = "/";  //除法
        private void textBox4_KeyDown(object sender, KeyEventArgs e)
        {
            double a = double.Parse(textBox1.Text); //用来存第一个数
            string symbol = textBox2.Text;          //用来存运算符
            double b = double.Parse(textBox3.Text); //用来存第二个数
            Context contex = null;                  //上下文
            if (symbol.Equals(AddSymbol))           //若为加号
            {
                contex = new Context(new Add());    //加法策略
            }
            else if (symbol.Equals(SubSymbol))      //如果减号
            {
                contex = new Context(new Sub());    //减法策略
            }
            else if (symbol.Equals(MulSymbol))      //若为乘号
            {
                contex = new Context(new Mul());    //乘法策略
            }
            else if (symbol.Equals(DivSymbol))      //若为除号
            {
                contex = new Context(new Div());    //除法策略
            }
            string answer = contex.Cal(a, b, symbol).ToString();  //用answer来存计算出来的答案,此时已经计算出a,b两个数的运算结果。
            if (e.KeyCode == Keys.Enter)              //回车操作
            {
                string result = textBox1.Text + textBox2.Text + textBox3.Text;//把运算式子存在result里面
                Count++;                                                      //出题总数加一
                if (textBox4.Text == answer)                                  //如果输入答案与计算出的answer相等
                {
                    MessageBox.Show("回答正确！");                            //弹出回答正确
                    listBox1.Items.Add(result + "=" + textBox4.Text.Trim() + "√");//并把运算式子存在listbox里
                    Right++;                                                  //答对题数加一
                }

                else                                                          //如果答错
                {
                    MessageBox.Show("答题错误！");                            //弹出答题错误
                    listBox1.Items.Add(result + "=" + textBox4.Text.Trim() +"×");//同样把运算式子放在listbox
                }
                label3.Text = "正确率：" + Convert.ToString(Right * 1.0 / Count * 100).PadRight(5, ' ').Substring(0, 5) + "%";//统计正确率
                textBox1.Clear();//把文本框清空，进行下一次出题
                textBox3.Clear();
                textBox4.Clear();
            }
        }
        private void button1_Click(object sender, EventArgs e)//保存按钮，把已答题目放在txt文件里
        {
            sfd.Filter = "(*.txt)|*.txt";
            if (sfd.ShowDialog() == DialogResult.OK)
            {
                string sPath = sfd.FileName;
                FileStream fs = new FileStream(sPath, FileMode.Create);
                StreamWriter sw = new StreamWriter(fs, Encoding.UTF8);
                int iCount = listBox1.Items.Count - 1;
                for (int i = 0; i <= iCount; i++)
                {
                    sw.WriteLine(listBox1.Items[i].ToString());
                }
                sw.Flush();
                sw.Close();
                fs.Close();
            }
        }
    }
}

 测试截图：