All 16 Exception Handling questions
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What is the difference between throw and throw ex inside a catch? What is the purpose of the finally block? What does the finally block guarantee, and when is it commonly used? When should you use using or await using? What are exception filters (when) and why use them? How do custom exception classes work in C#, and what's the recommended convention for creating one? What is exception filtering using the 'when' clause, and what advantage does it offer over catching and manually re-throwing? Why does 'throw;' (bare throw) preserve the original stack trace, while 'throw ex;' does not? When should you create custom exceptions vs use built-in ones? What is the recommended strategy for exceptions in a layered/enterprise app?
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C# › Exception Handling

How does a try/catch block work in C#, and what happens if no matching catch clause exists?

Beginner

Answer

Code in the try block runs normally; if it throws, execution jumps immediately to the FIRST matching catch clause (matched by exception type, checked top to bottom) — if no catch clause matches the thrown exception's type, the exception propagates up the call stack, potentially crashing the program if never caught anywhere.
try {
  int result = 10 / int.Parse("0");
} catch (DivideByZeroException ex) {
  Console.WriteLine($"Division error: {ex.Message}");
} catch (FormatException ex) {
  Console.WriteLine($"Format error: {ex.Message}");
}
Real-world example Gracefully handling a parsing error or division-by-zero condition instead of letting the application crash.

Common follow-ups: What happens if you put a more general exception type's catch clause BEFORE a more specific one?

Fundamentals
All 16 Exception Handling questions