一、首先建立PlusOperation類庫，其中包含抽象父類Operation，以及加、減、乘、除四個子類！

（1）父類Operation

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

namespace NameSpaceOperation
{
    public abstract class Operation
    {
        public int NumberOne { get
 
; set; }
        public int NubmerTwo { get; set; }
        public Operation(int a,int b)
        {
            this.NumberOne = a;
            this.NubmerTwo = b;

        }
        public abstract int GetResult();
    }
}

（2）加法子類Add

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

namespace NameSpaceOperation
{
    public class Add : Operation
    {
        public Add(int a, int b) : base(a, b)
        {
        }

        public override int GetResult()
        {
            return this.NumberOne + this.NubmerTwo;
        }
    }
}
 

（3）減法子類Sub

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

namespace NameSpaceOperation
{
    public class Sub : Operation
    {
        public Sub(int a, int b) : base(a, b)
        {
        }

        public override int GetResult()
        {
            return this.NumberOne - this.NubmerTwo;
        }
    }
}

（4）乘法子類Mul

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

namespace NameSpaceOperation
{
    public class Mul : Operation
    {
        public Mul(int a, int b) : base(a, b)
        {
        }

        public override int GetResult()
        {
            return this.NumberOne * this.NubmerTwo;
        }
    }
}

（5）除法子類Div

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


namespace NameSpaceOperation
{
    public class Div : Operation
    {
        public Div(int a, int b) : base(a, b)
        {
        }

        public override int GetResult()
        {
            return this.NumberOne / this.NubmerTwo;
        }
    }
}

二、建立專案SimpleFactoryPatternCalculator，引入PlusOperation類庫，新增NameSpaceOperation名稱空間

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

namespace SimpleFactoryPatternCalculator
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("請輸入你的第一個數字");
            int a = Convert.ToInt32(Console.ReadLine());
            Console.WriteLine("請輸入你的第二個數字");
            int b = Convert.ToInt32(Console.ReadLine());
            Console.WriteLine("請輸入你的運算子");
            string strOper = Console.ReadLine();
            Operation oper = GetOperation(strOper,a, b);
            if (oper!=null)
            {
                int result = oper.GetResult();
                Console.WriteLine("{0}{1}{2}={3}",a,strOper,b,result);
            }
            else
            {
                Console.WriteLine("沒有你需要的運算子");
            }

        }
        static Operation GetOperation(string oper,int a,int b)
        {
            Operation operation = null;
            switch (oper)
            {
                case "+":
                    operation = new Add(a, b);
                    break;
                case "-":
                    operation = new Sub(a, b);
                    break;
                case "*":
                    operation = new Mul(a, b);
                    break;
                case "/":
                    operation = new Div(a, b);
                    break;
            }
            return operation;
        }
    }
}