how to handle "DivideByZeroException" in c# ?

You can handle it the way you want. There are no common rules, but you should get to the root reason of the exception, using the debugger.

All you really need to know is the structured exception handling in general. Please see my past answers:
first of all, this one: Does Exception in C# Constructor Cause Caller Assignment to Fail?[^];
and also How do i make a loop that will stop when a scrollbar reaches the bottom[^],
Keep a c# windows form application running despite any unhandled exception[^],
When i run an application an exception is caught how to handle this?[^],
throw . .then ... rethrowing[^],
Handling exceptions in class library (dll)[^],
Exception Details: System.Runtime.InteropServices.COMException: Retrieving the COM class factory for component with CLSID {0006F03A-0000-0000-C000-000000000046} failed due to the following error:...[^].

—SA