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   源码介绍

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一个简单的计算器，虽然很简单。但是用心做了。对于非数字的提示与下一步(Tab)和焦点的控制 ，我是北大青鸟S1的学生

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace 课后练习3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            this.cmx1.SelectedIndex = 0;
        }
        private bool a = false;
        private bool b = false;
        private bool c = false;

        /// 验证是否输入为数字方法
        public bool isright(String number,ref String value) 
        {
            double i = 0;
            if (double.TryParse(number,out i))
            {
                value = number;
                return true;
            }
            else
            {
                value = "";
                return false;
            }
        }

        /// 计算
        private void button1_Click(object sender, EventArgs e)
        {
            c = false;
            String type = this.cmx1.Text;
            double value=0;      //结果
            if (a==true&&b==true)
            {
                //取出当前值
                double number1 = double.Parse(this.txt1.Text);
                double number2 = double.Parse(this.txt2.Text);
                switch (type)
                {
                    case " ":
                        value = number1   number2;
                        break;
                    case "-":
                        value = number1 - number2;
                        break;
                    case "*":
                        value = number1 * number2;
                        break;
                    case "/":
                        value = number1 / number2;
                        break;
                    default:
                        MessageBox.Show("运算符非法!", "温馨提示", MessageBoxButtons.OK, MessageBoxIcon.Error);
                        break;
                }
            }
            else
            {
                MessageBox.Show("请输入要计算的数值!","温馨提示",MessageBoxButtons.OK,MessageBoxIcon.Error);
            }
            this.txt3.Text = value.ToString();
            if (this.txt3.Text!=null)
            {
                c = true;
            }
        }

        /// 文本框1焦点离开事件
        private void txt1_Leave(object sender, EventArgs e)
        {
            String value = "";
            if ( isright(this.txt1.Text, ref value))
            {
                a = true;
            }
            else
            {
                a = false;
                lab5.Visible = true;
            }
            this.txt1.Text = value;
        }

        /// 文本框2焦点离开事件
        private void txt2_Leave(object sender, EventArgs e)
        {
            String value = "";
            if (isright(this.txt2.Text, ref value))
            {
                b = true;
            }
            else
            {
                b = false;
                lab5.Visible = true;
            }
            this.txt2.Text = value;
        }

        //两个文本框的进入事件，隐藏警示文本并清空显示结果
        private void txt_Enter(object sender, EventArgs e)
        {
            Control.CheckForIllegalCrossThreadCalls = false;
            txt3.Text = "";
            System.Timers.Timer t = new System.Timers.Timer(1000);
            t.Elapsed  = new System.Timers.ElapsedEventHandler(timer1_Tick);
            t.Enabled = true;
            t.AutoReset = false;
            if (this.ActiveControl==this.txt1&&c==true)
            {
                txt1.Text = "";
                txt2.Text = "";
            }
                
        }

        //组合框焦点到达
        private void cmx1_Enter(object sender, EventArgs e)
        {
            if (this.lab5.Visible == true)
            {
                this.txt1.Focus();
            }
        }

        //时钟执行事件
        private void timer1_Tick(object sender, EventArgs e)
        {
            lab5.Visible = false;
        }

        /// 计算按键的焦点到达
        private void button1_Enter(object sender, EventArgs e)
        {
            if (this.lab5.Visible == true)
            {
                this.txt2.Focus();
            }
        }

        //退出事件
        private void button2_Click(object sender, EventArgs e)
        {
            MessageBox.Show("谢谢使用");
            this.Close();
        }

        private void txt1_TextChanged(object sender, EventArgs e)
        {

        }
    }
}