Cannot implicitly convert type 'System.Windows.Forms.Control' to Combobox

[clflyer]

I have a small problem. I'm pretty much a newbie to C# coming out of VB.Net.
I have a windows form that has a GroupBox named grpSoldTo.
I want to be able to clear all the textboxes and comboxes that are in the GroupBox.
I know how to do it in VB.Net but when I try something similar in C# I get the following error:

Cannot implicitly convert type 'System.Windows .Forms.Control' to 'System.Windows .Forms.ComboBox '. An explicit conversion exists (are you missing a cast?)

Here is a snippet of my code:

 //Clear out the inputs
            ComboBox cmbo = default(ComboBox);

            foreach (Control ctrl in this.grpSoldTo.Controls) 
            {
	            if (ctrl.Name.StartsWith("txt")) 
                {
		            ctrl.Text = null;
	            }
                else if (ctrl.Name.StartsWith("cmbo"))
                {
                    cmbo = ctrl;
                    cmbo.SelectedIndex = 0;
                }
            }

The offending line is cmbo = ctrl;

Can anyone help?
Thanks,
Bill

[tlhintoq]

cmbo = ctrl;
                    cmbo.SelectedIndex = 0;

You have to cast the 'control' into a ComboBox

((ComboBox)ctrl).SelectedIndex = -1;

Also, to have nothing selected you want to set the selected index to -1, not zero. Remember that all lists are zero-indexed, meaning the first item is index 0, second item is index 1 and so on. -1 is the value of a combobox when nothing is selected.

[clflyer]

Thank you thats what I needed.
I also discovered that I could do this:
cmbo = (ComboBox)ctrl;
cmbo.SelectedIn dex=-1

Thanks for the quick response.

[tlhintoq]

You can. But why create the extra cmbo object if you don't need to?
Glad I could help

[GaryTexmo]

Another option you can use is the "as" operator... I like to use it when casting like this since you don't know if an object can be cast or not.

ComboBox theComboBox = theControl as ComboBox;
if (theComboBox != null)
{
  // whatever you would do if the control is a combobox, using theComboBox
}

You can also actually use the is operator to test...

if (theControl is ComboBox)
{
  // whatever you would do if the control is a combobox, using (ComboBox)theControl
}

Just helps make things a little safer. For example, if your controls contain a button with a name that starts with "cmbo", I believe your code will throw an exception.