题目：

设计一个简单计算器

思路：

首先在应用框体中设计自己喜欢的计算器格式，接着编辑其中的函数。抽取一个Call函数用来显示从键盘输入的数字，cleanall()函数进行清屏操作，mode（）函数进行四则运算，switchmode()函数显示符号，最后将结果输出即可。

示例代码：

using System;
using System.Windows.Forms;
namespace Calculator
{
    public partial class FormMain : Form
    {
        double number1 = 0,number2 = 0,result;
        int inputnumber;
        enum Operator { none,plus,minus,multiplication,division}
        Operator mode = Operator.none;
        bool isequal = false;
        public FormMain()
        {
            InitializeComponent();
        }
        private void button1_Click(object sender, EventArgs e)
        {
            inputnumber =4;
            call(inputnumber);
        }
      private void button4_Click(object sender, EventArgs e)
        {
            inputnumber = 1;
            call(inputnumber);
        }
        private void button16_Click(object sender, EventArgs e)
        {
            inputnumber = 9;
            call(inputnumber);
        }
        private void button2_Click(object sender, EventArgs e)
        {
            inputnumber = 5;
            call(inputnumber);
        }
        private void button3_Click(object sender, EventArgs e)
        {
            inputnumber = 6;
            call(inputnumber);
        }
        private void button5_Click(object sender, EventArgs e)
        {
            inputnumber =2;
            call(inputnumber);
        }
        private void button6_Click(object sender, EventArgs e)
        {
            inputnumber =3;
            call(inputnumber);
        }
        private void button7_Click(object sender, EventArgs e)
        {
            inputnumber = 0;
            call(inputnumber);
        }
        private void button12_Click(object sender, EventArgs e)
        {
            mode = Operator.plus;
            switchmode();
        }
        private void button11_Click(object sender, EventArgs e)
        {
            mode = Operator.minus;
            switchmode();
        }
        private void button10_Click(object sender, EventArgs e)
        {
            mode = Operator.multiplication;
            switchmode();
        }
        private void button9_Click(object sender, EventArgs e)
        {
            mode = Operator.division;
            switchmode();
        }
        private void button8_Click(object sender, EventArgs e)
        {
            switch (mode)
            {
                case Operator.plus:
                    result = number1 + number2;
                    break;
                case Operator.minus:
                    result = number1 - number2;
                    break;
                case Operator.multiplication:
                    result = number1 * number2;
                    break;
                case Operator.division:
                    result = number1 / number2;
                    break;
            }
            number1 = 0;
            number2 = 0;
            isequal = true;
            labelbefore.Text = " ";
            labelmode.Text = " ";
       labelout.Text = Convert.ToString(result);
        }
        private void button14_Click(object sender, EventArgs e)
        {
            inputnumber = 8;
            call(inputnumber);
        }
        private void button13_Click(object sender, EventArgs e)
        {
            inputnumber = 7;
            call(inputnumber);
        }
        private void button15_Click(object sender, EventArgs e)
        {
            cleanall();
        }
        public void call(int an)
        {
            if (mode == Operator.none)
            {
                number1 = number1 * 10 + an;
                labelout.Text = Convert.ToString(number1);
            }
            else
            {
                number2 = number2 * 10 + an;
                labelout.Text = Convert.ToString(number2);
            }
        }
        private void labelout_Click(object sender, EventArgs e)
        {
            labelout.Text = Convert.ToString(number1);
        }
        public void cleanall()
        {
            number1 = 0;
            number2 = 0;
            labelout.Text = Convert.ToString(number1);
            labelbefore.Text = " ";
            labelmode.Text = " ";
            isequal = false;
            mode = Operator.none;
        }
        public void switchmode()
        {
            switch (mode)
            {
                case Operator.plus:
                     labelmode.Text = "+";
                     break;
                case Operator.minus:
                    labelmode.Text = "-";
                    break;
                case Operator.multiplication:
                    labelmode.Text = "x";
                    break;
                case Operator.division:
                    labelmode.Text = "/";
                    break;
            }
            if(isequal == true)
            {
                number1 = result;
            }
            labelbefore.Text = Convert.ToString(number1);
            labelout.Text = Convert.ToString(number2);
           
        }
    }
}

测试：