C# 5.0 Programmer's Reference

Chapter 10 ❘ 655
The button’s event handler does all its work inside a try-catch block. The first two catch
sections display messages that the user can understand. The third catch section handles unexpected
exceptions. Because it doesn’t know what kinds of exceptions to expect, it can’t display
a user-friendly message. Instead it just writes the exception’s name into the Console window
(so you can add a catch section for it) and displays the exception’s message to the user.
The Factorial function throws an ArgumentOutOfRangeException if its parameter
is negative. It then uses a checked block to watch for arithmetic errors and calculates the
factorial. (See the section “Casting Numbers” in Chapter 4, “Data Types, Variables, and
Constants,” for a review of checked blocks.)
Chapter 10
1. The TraceFactorial example program, which is available in this book’s downloads,
includes code for Exercises 1, 2, and 4. It uses the following code to solve Exercise 1.
(Notice how the code needs to separate the recursive call from the return statement so
that it can display the method’s result before returning.)
private long Factorial(long number)
{
Debug.WriteLine("Factorial(" + number.ToString() + ")");
Debug.Indent();
long result;
if (number