设计模式——简单工厂模式

1. 通过封装、继承、多态把程序的耦合度降低。用设计模式使得程序更加的灵活，容易修改，并且易于复用。
2. 让业务逻辑和界面逻辑分开，让它们耦合度降低，这样才容易维护和扩展。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;//要求输入两个数和运算符号，得到结果namespace Calculator
{class Program{static void Main(string[] args){Console.WriteLine("请输入一个数字");string strNum1 = Console.ReadLine();Console.WriteLine("请在输入一个数字");string strNum2 = Console.ReadLine();Console.WriteLine("请输入一个运算符");string strOp = Console.ReadLine();Operation oper = OperationFactory.CreateOperation(strOp);double num1 = double.Parse(strNum1);double num2 = double.Parse(strNum2);double result = oper.GetResult(num1, num2);Console.WriteLine($"{num1}{strOp}{num2}={result}");}}public class Operation{private double _numberA = 0;private double _numberB = 0;public double NumberA{get{return _numberA;}set{_numberA = value;}}public double NumberB{get{return _numberB;}set{_numberB = value;}}public virtual double GetResult(double num1,double num2){return 0;}}class CalculateAdd : Operation{public override double GetResult(double num1, double num2){return num1 + num2;}}class CalculateSub : Operation{public override double GetResult(double num1, double num2){return num1 - num2;}}class CalculateMulti : Operation{public override double GetResult(double num1, double num2){return num1 * num2;}}class CalculateDiv : Operation{public override double GetResult(double num1, double num2){try{return num1 / num2;}catch (Exception ex){throw ex;}       }}public class OperationFactory{static Operation oper = null;public static Operation CreateOperation(string op){switch (op){case "+":oper = new CalculateAdd();break;case "-":oper = new CalculateSub();break;case "*":oper = new CalculateMulti();break;case "/":oper = new CalculateDiv();break;default:break;}return oper;}}}