using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Text; using System.Windows.Forms;  namespace WindowsApplication1 {   public partial class Main : Form   {     public Main()     {       InitializeComponent();     }      private void Main_Load(object sender, EventArgs e)     {      }      private void txtInshu1_TextChanged(object sender, EventArgs e)     {      }      private void txtInshu1_KeyPress(object sender, KeyPressEventArgs e)     {       OnlyEnterNumber(sender, e);     }      //// <summary>     /// 只能輸入數字（含負號小數點）     /// </summary>     /// <param name="sender"></param>     /// <param name="e"></param>     public static void OnlyEnterNumber(object sender, KeyPressEventArgs e)     {       if ((e.KeyChar < 48 || e.KeyChar > 57) && e.KeyChar != 8 && e.KeyChar != 13 && e.KeyChar != 45 && e.KeyChar != 46)       {         e.Handled = true;       }        // 輸入為負號時，只能輸入一次且只能輸入一次       if (e.KeyChar == 45 && (((TextBox)sender).SelectionStart != 0 || ((TextBox)sender).Text.IndexOf("-") >= 0)) e.Handled = true;       if (e.KeyChar == 46 && ((TextBox)sender).Text.IndexOf(".") >= 0) e.Handled = true;     }       /*      * 參數：d表示要四舍五入的數；i表示要保留的小數點后位數。      * 正負數都四舍五入，適合數據統計的顯示      */     double Round(double d, int i)     {       if (d >= 0)       {         d += 5 * Math.Pow(10, -(i + 1));       }       else       {         d += -5 * Math.Pow(10, -(i + 1));       }       string str = d.ToString();       string[] strs = str.Split('.');       int idot = str.IndexOf('.');       string prestr = strs[0];       string poststr = strs[1];       if (poststr.Length > i)       {         poststr = str.Substring(idot + 1, i);       }       string strd = prestr + "." + poststr;       d = Double.Parse(strd);       return d;     }      private void txtInshu2_TextChanged(object sender, EventArgs e)     {      }      private void txtInshu2_KeyPress_1(object sender, KeyPressEventArgs e)     {       OnlyEnterNumber(sender, e);     }      private void btnJisuan_Click(object sender, EventArgs e)     {       if (txtInshu1.Text == "") {         MessageBox.Show("因數1不能為空！", "警告", MessageBoxButtons.OK, MessageBoxIcon.Warning);         return;       }       if (txtInshu2.Text == "")       {         MessageBox.Show("因數2不能為空！", "警告", MessageBoxButtons.OK, MessageBoxIcon.Warning);         return;       }        double inshu1 = Convert.ToDouble(txtInshu1.Text);       double inshu2 = Convert.ToDouble(txtInshu2.Text);       double result = 0.0;        if (radioBtnJia.Checked) {         result = inshu1 + inshu2;       }        if (radioBtnJian.Checked)       {         result = inshu1 - inshu2;       }        if (radioBtnCheng.Checked)       {         result = inshu1 * inshu2;       }        if (radioBtnChu.Checked)       {         if (0 == inshu2)         {           MessageBox.Show("因數2做除數不能為0！", "警告", MessageBoxButtons.OK, MessageBoxIcon.Warning);           return;         }         result = inshu1 / inshu2;         result = Round(result, 6);       }        txtResult.Text = Convert.ToString(result);     }   } }