2018-12-13加减乘除

        double  result = 0;
        Console.Write("请选择一种运算：1、加法 2、减法 3、乘法 4、除   法"+"\n");
        Console.Write("请选择算法：");
        double  a = Convert.ToInt32(Console.ReadLine ());
        Console.WriteLine("请输入第一个数字：");
        double  b = Convert.ToInt32(Console.ReadLine());
        Console.WriteLine("请输入第二个数字：");
        double  c = Convert.ToInt32(Console .ReadLine ());

        
        if(a==1)
        {
            result = b + c;
            
        }
        if (a==2)
        {
            if(c>b)
            {
                double  temp = 0;
                temp = c;
                c = b;
                b = temp;
            }
            result = b- c;
        }
        if(a==3)
        {
            result = b * c;
        }
        if(a==4)
        {
            if(c>b)
            {
                double  t = 0;
                t = c;
                c = b;
                b = t;
            }
            result = b / c;
        }
        Console.WriteLine();

        Console.WriteLine("*********运算结果是：{0}",result);
        Console.ReadKey();

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