C#中foreach问题
代码如下：
[code=C#][/code]
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace label_use
{
  public partial class Form1 : Form
  {
  public Form1()
  {
  InitializeComponent();
  }

  private void Form1_Load(object sender, EventArgs e)
  {
  for (int i = 1900; i <= 2050; i++)
  {
  comboBox1.Items.Add(i);
  }
  comboBox1.Text = DateTime.Now.Year.ToString();

  }

  private void label2_Click(object sender, EventArgs e)
  {

  }

  private void textBox1_TextChanged(object sender, EventArgs e)
  {

  }

  private void label1_Click(object sender, EventArgs e)
  {
   
  }

  private void button1_Click(object sender, EventArgs e)
  {
   
  }

  private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
  {
  int intyear = Convert.ToInt32(comboBox1.Text);
  string strtext = "";
  switch (intyear %12)
  {
  case 4:
  strtext="鼠";
  break;
  case 5:
  strtext = "牛";
  break;
  case 6:
  strtext = "虎";
  break;
  case 7:
  strtext = "兔";
  break;
  case 8:
  strtext = "龙";
  break;
  case 9:
  strtext = "蛇";
  break;
  case 10:
  strtext = "马";
  break;
  case 11:
  strtext = "羊";
  break;
  case 0:
  strtext = "猴";
  break;
  case 1:
  strtext = "鸡";
  break;
  case 2:
  strtext = "狗";
  break;
  case 3:
  strtext = "猪";
  break;
  }
  foreach (RadioButton rbtn in groupBox1 .Controls )
  {
  if (rbtn.Text==strtext)
  {
  rbtn.Checked = true;
  }
   
  }

  }

  private void RadioButton4_CheckedChanged(object sender, EventArgs e)
  {

  }

  private void radioButton12_CheckedChanged(object sender, EventArgs e)
  {

  }
  }
}
问题在如下图：
在调试是为什么会出现“当从一个数字执行强制转换时,值必须是一个小于无限大的数字”这样的排错提示呢？求解。

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