1. Debugging and Handling Exceptions
Chapter 11
Presented by Rodion Karmazin

2. !!Beforehand Warning!!
None of the content in this PowerPoint belongs to me. All rights for the content go to their respective owners.

3. Quick Summary
What you shall learn from this HUGE chapter are the “Try”, “Catch”, and “Finally” methods.
Also you shall find out what debugging really is.
I will also do my best to explain something about Exceptions

4. Error message does not always state the correct problem
Errors
Visual Studio IDE reports errors as soon as it is able to detect a problem
Syntax errors
Language rule violation
Error message does not always state the correct problem
Quick info
Figure 11-1 Syntax error – extraneous semicolon

5. Run-Time Errors
Just because your program reports no syntax errors does not necessarily mean it is running correctly
One form of run-time error is a logic error
Program runs, but produces incorrect results
May be off-by-one in a loop
Sometime users enter incorrect values
Finding the problem can be challenging

6. “Exceptions” Some circumstances are beyond programmer’s control
You have assumed nothing unusual would occur
Have probably experienced unhandled exceptions being thrown
While you browsed Web pages
Unless provisions are made for handling exceptions, your program may crash or produce erroneous results
Unhandled exception

7. “Exceptions” example
Dialog box asks you whether you want to have an error report sent to Microsoft
Figure 11-9 Microsoft error reporting

8. “Exceptions” example cont.
Message displayed when you are creating console application and unhandled exception occurs
Figure Unhandled exception in a console application

9. “Unhandled Exceptions”
Selecting Debug>Start to run application in Visual Studio
Yellow arrow marks the error
erroneous code highlighted
Figure Unhandled exception thrown – dividing by zero

10. Raising an “Exception”
Error encountered – no recovery
Raise or throw an exception
Execution halts in the current method and the “Common Language Runtime” or “CLR” attempts to locate an “exception handler”
Exception handler: block of code to be executed when a certain type of error occurs
If no exception handler is found in current method, exception is thrown back to the calling method

11. Exception-Handling Techniques
If event creates a problem frequently, best to use conditional expressions to catch and fix problem
Execution is slowed down when CLR has to halt a method and find an appropriate event handler
Exception-handling techniques are for serious errors that occur infrequently
Exceptions classes integrated within the FCL
Used with the try…catch…finally program constructs
.NET Framework Class Library

12. Try…Catch…Finally Blocks
Code that may create a problem is placed in the try block
Code to deal with the problem (the exception handler) is placed in catch blocks
Catch clause
Code to be executed whether an exception is thrown or not is placed in the finally block

13. catch [ (ExceptionClassName exceptionIdentifier) ]
try {
// Statements }
catch [ (ExceptionClassName exceptionIdentifier) ]
// Exception handler statements
: // [additional catch clauses]
[ finally
} ]
Notice square brackets indicate optional entry
One catch clause required
finally clause optional

14. Try…Catch…Finally Blocks (continued)
Generic catch clause
Omit argument list with the catch
Any exception thrown is handled by executing code within that catch block
Control is never returned into the try block after an exception is thrown
Using a try…catch block can keep the program from terminating abnormally

15. Use of Generic Catch Clause
This example uses a generic catch block
Figure Generic catch block handles the exception

16. // calculate average grade for a class int totalGrades = 0; int grade = 0; int sumGrades = 0; String data = ""; Console.WriteLine("Please enter a grade [## to end]"); while (true) { try { data = Console.ReadLine(); grade = int.Parse(data); sumGrades += grade; totalGrades++; } catch (Exception e) if (data == "##") break; Console.WriteLine("Invalid data - try again"); Console.WriteLine("Please enter a grade [## to end]"); if (totalGrades > 0) Console.WriteLine("Average grade is {0:F2}", sumGrades / totalGrades); else Console.WriteLine("Average = 0 (No data was supplied)");

17. Comments, complaints, suggestions are also inquired for at this time!
Any Questions?
Comments, complaints, suggestions are also inquired for at this time!
!!!!!!!!
READ
THE
BOOK

18. Assignments (5 Pointer) (10 Pointer)
Make a program that requests a phone number. If a knucklehead runs the program and types in a letter, display an error message. “Try” and “Catch” are required for this.
(10 Pointer)
Try to make out whatever is happening on slide 16 and make a program that asks for the number of scores and has the user put in the scores. If there is an error in the input, address that error immediately with a message box or Console.Writeline();