How to STOP execution of btn_Click event based on a condition

Hi
I am sure that this query has been answered on forums earlier. I could not find the right solution and forced myself to post here.
Question
I have an <asp:panel> that contains number of controls (i.e., TextBoxes and DropDownLists) I want to STOP the execution of btn_Click event if all the TextBoxes Text and DropDownList selectedItem = 0. In other words 'the end user not entered anything in Text boxes and selected any drop down lists on the page.
I have below source code that loops through the controls within panel.
foreach(Control c in searchPanel.Controls) { //if(((TextBox)(c)).Text == }
Your help is appreciated.
Thanks,
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