C# 4 and .NET 4

Catching exceptions ❘ 355
Now your try block looks like this:
try
{
// code for normal execution
if (Overflow == true)
{
throw new OverflowException();
}
// more processing
if (OutOfBounds == true)
{
throw new IndexOutOfRangeException();
}
// otherwise continue normal execution
}
catch (OverflowException ex)
{
// error handling for the overflow error condition
}
catch (IndexOutOfRangeException ex)
{
// error handling for the index out of range error condition
}
finally
{
// clean up
}
So far, this might not look that much different from what you could have done a long time ago if you ever
used the Visual Basic 6 On Error GoTo statement (with the exception perhaps that the different parts in the
code are separated). C#, however, provides a far more powerful and flexible mechanism for error handling.
This is because you can have throw statements that are nested in several method calls inside the try block,
but the same try block continues to apply even as execution flow enters these other methods. If
the computer encounters a throw statement, it immediately goes back up through all the method calls on the
stack, looking for the end of the containing try block and the start of the appropriate catch block. During
this process, all the local variables in the intermediate method calls will correctly go out of scope. This
makes the try...catch architecture well suited to the situation described at the beginning of this section,
where the error occurs inside a method call that is nested inside 15 or 20 method calls, and processing has
to stop immediately.
As you can probably gather from this discussion, try blocks can play a very significant part in controlling
the flow of execution of your code. However, it is important to understand that exceptions are intended for
exceptional conditions, hence their name. You wouldn’t want to use them as a way of controlling when to
exit a do...while loop.
implementing multiple Catch blocks
The easiest way to see how try...catch...finally blocks work in practice is with a couple of examples.
The first example is called SimpleExceptions. It repeatedly asks the user to type in a number and then
displays it. However, for the sake of this example, imagine that the number has to be between 0 and
5; otherwise, the program won’t be able to process the number properly. Therefore, you will throw an
exception if the user types in anything outside of this range.
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