/// <summary>
  /// 限制输入数字以外的字符
  /// </summary>
  /// <param name="sender"></param>
  /// <param name="e"></param>
  private void textbox_KeyPress(object sender, KeyPressEventArgs e)
  {
  if (((int)e.KeyChar < 48 || (int)e.KeyChar > 57) && e.KeyChar != 8)
  {
  e.Handled = true;
  }
  }

------解决方案--------------------
   try
           {
             int num= int.Parse(txtnum.Text);
           }
           catch (Exception ex)
           {
               MessageBox.Show("非数字！");
           }