TextBox在乘法表中設置錯誤

Question

我在C＃中製作了一個乘法表程序，供學生學習。這是我想要今晚完成的課程項目。

問題是，當我按'檢查答案'按鈕，錯誤「輸入字符串不是在一個正確的格式。」被拋出。

這是我的代碼;它是一個詳細的。檢查文本框的答案是否正確時，會引發錯誤。我還沒有找到修復程序。如果您有任何建議或修正，請告訴我。

感激， 克萊頓

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Web; 
using System.Web.UI; 
using System.Web.UI.WebControls; 

public partial class ContentPages_MySecondCalculator : System.Web.UI.Page 
{ 
    int SelectedNum = 0; 

    protected void Page_Load(object sender, EventArgs e) 
    { 

    } 
    protected void btnTimesTable_Click(object sender, EventArgs e) 
    { 
     /*protects against incorrect input **/ 


      int SelectedNum = 0; 

      switch (drpNumberList.SelectedValue) 
      { 
       case "1": 
        SelectedNum = 1; 
        break; 
       case "2": 
        SelectedNum = 2; 
        break; 
       case "3": 
        SelectedNum = 3; 
        break; 
       case "4": 
        SelectedNum = 4; 
        break; 
       case "5": 
        SelectedNum = 5; 
        break; 
       case "6": 
        SelectedNum = 6; 
        break; 
       case "7": 
        SelectedNum = 7; 
        break; 
       case "8": 
        SelectedNum = 8; 
        break; 
       case "9": 
        SelectedNum = 9; 
        break; 
       case "10": 
        SelectedNum = 10; 
        break; 
       case "11": 
        SelectedNum = 11; 
        break; 
       case "12": 
        SelectedNum = 12; 
        break; 

      } 

      /* the first list of numbers are set to their values here **/ 
      lbl1.Text = SelectedNum.ToString(); 
      lbl1b.Text = SelectedNum.ToString(); 
      lbl1c.Text = SelectedNum.ToString(); 
      lbl1d.Text = SelectedNum.ToString(); 
      lbl1e.Text = SelectedNum.ToString(); 
      lbl1f.Text = SelectedNum.ToString(); 
      lbl1g.Text = SelectedNum.ToString(); 
      lbl1h.Text = SelectedNum.ToString(); 
      lbl1i.Text = SelectedNum.ToString(); 
      lbl1j.Text = SelectedNum.ToString(); 
      lbl1k.Text = SelectedNum.ToString(); 
      lbl1l.Text = SelectedNum.ToString(); 

      /* the second list of numbers that appears are set to their values here **/ 
      lbl2a.Text = "1"; 
      lbl2b.Text = "2"; 
      lbl2c.Text = "3"; 
      lbl2d.Text = "4"; 
      lbl2e.Text = "5"; 
      lbl2f.Text = "6"; 
      lbl2g.Text = "7"; 
      lbl2h.Text = "8"; 
      lbl2i.Text = "9"; 
      lbl2j.Text = "10"; 
      lbl2k.Text = "11"; 
      lbl2l.Text = "12"; 




     } 
      // in case no input was taken 



    protected void lblNumberList_SelectedIndexChanged(object sender, EventArgs e) 
    { 

    } 
    /* 
    protected void txtBox1_TextChanged(object sender, EventArgs e) 
    { 

    } 
    * */ 

    protected void btnCheckAnswers_Click(object sender, EventArgs e) 
    { 
     if (true) 
     { 
      lblFeedback1.Text = "correct"; 
     } 
     else 
     { 
      lblFeedback1.Text = "incorrect"; 
     } 
     if (true) 
     { 
      lblFeedback2.Text = "correct"; 
     } 
     else 
     { 
      lblFeedback2.Text = "incorrect"; 
     } 
     if (true) 
     { 
      lblFeedback3.Text = "correct"; 
     } 
     else 
     { 
      lblFeedback3.Text = "incorrect"; 
     } 
     if (true) 
     { 
      lblFeedback4.Text = "correct"; 
     } 
     else 
     { 
      lblFeedback4.Text = "incorrect"; 
     } 
     if (true) 
     { 
      lblFeedback5.Text = "correct"; 
     } 
     else 
     { 
      lblFeedback5.Text = "incorrect"; 
     } 
     if (true) 
     { 
      lblFeedback6.Text = "correct"; 
     } 
     else 
     { 
      lblFeedback6.Text = "incorrect"; 
     } 
     if (true) 
     { 
      lblFeedback7.Text = "correct"; 
     } 
     else 
     { 
      lblFeedback7.Text = "incorrect"; 
     } 
     if (true) 
     { 
      lblFeedback8.Text = "correct"; 
     } 
     else 
     { 
      lblFeedback8.Text = "incorrect"; 
     } 
     if (true) 
     { 
      lblFeedback9.Text = "correct"; 
     } 
     else 
     { 
      lblFeedback9.Text = "incorrect"; 
     } 
     if (true) 
     { 
      lblFeedback10.Text = "correct"; 
     } 
     else 
     { 
      lblFeedback10.Text = "incorrect"; 
     } 
     if (true) 
     { 
      lblFeedback11.Text = "correct"; 
     } 
     else 
     { 
      lblFeedback11.Text = "incorrect"; 
     } 
     if (true) 
     { 
      lblFeedback12.Text = "correct"; 
     } 
     else 
     { 
      lblFeedback12.Text = "incorrect"; 
     } 

     /* 
     if ((Convert.ToInt32(txtBox1.ToString())) == SelectedNum) 
     { 

     } 
     if ((Convert.ToInt32(txtBox2.ToString())) == SelectedNum * 2) 
     { 

     } 
     if ((Convert.ToInt32(txtBox2.ToString())) == SelectedNum * 3) 
     { 

     } 
     if ((Convert.ToInt32(txtBox2.ToString())) == SelectedNum * 4) 
     { 

     } 
     if ((Convert.ToInt32(txtBox2.ToString())) == SelectedNum * 5) 
     { 

     } 
     if ((Convert.ToInt32(txtBox2.ToString())) == SelectedNum * 6) 
     { 

     } 
     if ((Convert.ToInt32(txtBox2.ToString())) == SelectedNum * 7) 
     { 

     } 
     if ((Convert.ToInt32(txtBox2.ToString())) == SelectedNum * 8) 
     { 

     } 
     if ((Convert.ToInt32(txtBox2.ToString())) == SelectedNum * 9) 
     { 

     } 
     if ((Convert.ToInt32(txtBox2.ToString())) == SelectedNum * 10) 
     { 

     } 
     if ((Convert.ToInt32(txtBox2.ToString())) == SelectedNum * 11) 
     { 

     } 
     if ((Convert.ToInt32(txtBox2.ToString())) == SelectedNum * 12) 
     { 

     } 
     * */ 
    } 
    } 

Answer 1

你所得到的錯誤是，當你試圖將一個無效的字符串轉換爲int。例如：

Convert.ToInt32("asdf"); 

會拋出此錯誤，因爲asdf無法轉換爲有效數字。下面將不會拋出這個錯誤：

Convert.ToInt32("123"); 

我建議使用Int32.TryParse http://msdn.microsoft.com/en-us/library/f02979c7.aspx

此功能是專門推出以防止拋出的異常。下面是它的用法示例：

int number; 
    bool result = Int32.TryParse(value, out number); 
    if (result) 
    { 
    Console.WriteLine("Converted '{0}' to {1}.", value, number);   
    } 
    else 
    { 
    if (value == null) value = ""; 
    Console.WriteLine("Attempted conversion of '{0}' failed.", value); 
    }