C#

foreach(Control ctl in panel1.Controls)
{
    CheckBox chk = ctl as CheckBox;
    if(chk == null)
        continue;
 
    // Do whatever with the check box here
}

if(ctl is CheckBox)
{
    CheckBox chk = (CheckBox) ctl;
 
    ...
}

<br />
foreach(Control ctrl in mainPanel.Controls)<br />
{<br />
  Panel p = ctrl as Panel;<br />
  if(p == null) continue;<br />
  else<br />
  {<br />
      foreach(Control ctl in p.Controls)<br />
      {<br />
          CheckBox chk = ctl as CheckBox;<br />
	  if(chk == null) continue;<br />
	  else<br />
	  {<br />
            if(chk.Text == "Check All" || chk.Text == "Uncheck All") continue;<br />
else<br />
{<br />
	     if(chk.Checked)<br />
	     {<br />
	        sql += " " + chk.Text + "=1,";<br />
	     }<br />
	     else<br />
             {<br />
		sql += " " + chk.Text + "=0,";<br />
	     }<br />
}<br />
          }<br />
   }<br />
}<br />
}

foreach(Control ctrl in mainPanel.Controls)
{
    Panel p = ctrl as Panel;
    if(p == null)
        continue;
 
    foreach(Control ctl in p.Controls)
    {
        CheckBox chk = ctl as CheckBox;
        if(chk == null)
            continue;
 
        if(chk.Text == "Check All" || chk.Text == "Uncheck All")
            continue;
 
        if(chk.Checked)
        {
            sql += " " + chk.Text + "=1,";
        }
        else
        {
            sql += " " + chk.Text + "=0,";
        }
    }
}

private int selectedTab = 0;
private int newTab      = -1;
 
private void tabControl1_SelectedIndexChanged(object sender, System.EventArgs e)
{
    // Don't allow nesting in the handler
    if(tabControl1.SelectedIndex == selectedTab ||
        tabControl1.SelectedIndex == newTab)
        return;
 
    // Return tu current tab
    newTab = tabControl1.SelectedIndex;
    tabControl1.SelectedIndex = selectedTab;
 
    // Perform the validation
    if(DialogResult.Yes == MessageBox.Show(this, "Sure?", "??",
        MessageBoxButtons.YesNo))
    {
        // Validation passed, go to new tab
        tabControl1.SelectedIndex = newTab;
        selectedTab = tabControl1.SelectedIndex;
    }
 
    newTab = -1;
}

/// <summary>
/// Delegate that defines a handler for the SelectedIndexChanging event.
/// </summary>
public delegate void TabControlCancelEventHandler(object sender,
    TabControlCancelEventArgs e);
 
/// <summary>
/// Derived tab control that adds SelectedIndexChanging event.
/// </summary>
public class TabControlEx : TabControl
{
    /// <summary>
    /// Fired when the selected tab is about to change, allowing the
    /// receiver of the event to cancel.
    /// </summary>
    public event TabControlCancelEventHandler SelectedIndexChanging;
 
    /// <summary>
    /// Default constructor. Initializes a new TabControlEx object.
    /// </summary>
    public TabControlEx() 
    {
    }
 
    /// <summary>
    /// Called when index has changed. Raises SelectedIndexChanged event.
    /// </summary>
    /// <param name="e">Event arguments.</param>
    protected override void OnSelectedIndexChanged(EventArgs e)
    {
        // Disallow nesting of this event
        if(newTab != -1)
            return;
 
        try
        {
            // Save new tab, and return tu current tab
            newTab = SelectedIndex;
            SelectedIndex = selectedTab;
 
            // Raise SelectedIndexChanging event
            TabControlCancelEventArgs e2 = new TabControlCancelEventArgs(newTab);
            OnSelectedIndexChanging(e2);
 
            // If user chose to cancel, stay in current tab
            if(e2.Cancel)
                return;
 
            // Now we can select the requested tab
            SelectedIndex = newTab;
            selectedTab = SelectedIndex;
 
            // Finally call registered event handlers
            base.OnSelectedIndexChanged(e);
        }
        finally
        {
            newTab = -1;
        }
    }
 
    /// <summary>
    /// Raises SelectedIndexChanging event.
    /// </summary>
    /// <param name="e">Event arguments.</param>
    protected virtual void OnSelectedIndexChanging(TabControlCancelEventArgs e)
    {
        // If any handler is registered, raise the event
        if(SelectedIndexChanging != null)
            SelectedIndexChanging(this, e);
    }
 
    private int selectedTab = 0;
    private int newTab      = -1;
}
 
/// <summary>
/// Contain arguments for TabControlEx's SelectedIndexChanging event.
/// </summary>
public class TabControlCancelEventArgs : CancelEventArgs
{
    /// <summary>
    /// Constructor. Initializes a new TabControlCancelEventArgs.
    /// </summary>
    /// <param name="tab">Index of tab page that will be selected.</param>
    public TabControlCancelEventArgs(int tab)
        : base()
    {
        this.tab = tab;
    }
 
    /// <summary>
    /// Constructor. Initializes a new TabControlCancelEventArgs.
    /// </summary>
    /// <param name="tab">Index of tab page that will be selected.</param>
    /// <param name="cancel">true to cancel the selection change,
    /// false to allow it.</param>
    public TabControlCancelEventArgs(int tab, bool cancel)
        : base(cancel)
    {
        this.tab = tab;
    }
 
    /// <summary>
    /// Gets the index of the tab page that will be selected.
    /// </summary>
    public int Tab
    {
        get { return tab; }
    }
 
    private int tab;
}

myTab.SelectedIndexChanging += new TabControlCancelEventHandler(myTab_SelectedIndexChanging);

private void myTabSelectedIndexChanging(object sender, TabControlCancelEventArgs e)
{
    if(validation fails)
        e.Cancel = true;
}