1. Finding and Debugging Errors

2. Categories of Errors Syntax errors are detected at compile time
Use the Error List window to find these errors
The debugging tools cannot help with syntax errors
Runtime errors occur as an application executes
Logic errors cause an application to produce unexpected results but do not cause exceptions

3. Types of Runtime Errors
File processing errors
Arithmetic errors
Null reference errors
And many more

4. File Processing Errors
Sequential files with extra trailing carriage returns will generate errors
Sequential files with extra or missing fields will also cause errors
Omitting the carriage return on the last record may cause the last record to be ignored

5. Arithmetic Errors (1)
Numeric overflow results in the following exception:
Correct by performing double precision arithmetic instead of integer arithmetic

6. Arithmetic Errors (2)
Trying to convert an invalid value to a number will result in a System.FormatException
Call TryParse() to test before conversion

7. Arithmetic Errors (3)
Integer division by zero throws a System.DivideByZeroException:
Fix by testing the dividend value

8. Arithmetic Errors (4)
Division by zero is handled differently for floating point numbers and floating point division
Division by zero results in the value Infinity
Test using
Double.IsInfinity(Value)

9. Null Reference Errors (Introduction)
Pure and simple, you reference an object with first creating an instance of that object
The following exception is thrown

10. Interrogating the Value of a Variable or Property
Do while the application is in break mode
In the Code Editor, highlight the variable, object, or property
Expand or collapse complex objects as necessary

11. Interrogating the Value of a Variable or Property (Example)

12. Setting Breakpoints (1)
Use to temporarily suspend execution while a program runs
Multiple breakpoints may be set
Breakpoints may be enabled or disabled
It’s possible to clear all breakpoints
Breakpoints are persistent between invocations of Visual Studio

13. Setting Breakpoints (2)
Set simple breakpoints on a line by clicking in the left margin in the Code Editor
A maroon circle appears in the left margin
Breakpoints may be set only on executable statements because declaration statements don’t execute!

14. Setting Breakpoints (3)
Breakpoints appear in the Breakpoints window

15. Setting Conditional Breakpoints
Break when a condition becomes true or a value changes
Use for problems having long iteration counts

16. Setting Hit Count Breakpoints
Break on an iteration count
Hit count breakpoints are configurable
Break after 999 iterations

17. Setting Conditional Breakpoints
Conditional breakpoints are hit when
The value of a Boolean condition is True
The value of a condition has changed

18. Setting Conditional Breakpoints (Illustration)
Set a conditional breakpoint

19. Setting WatchPoints There are multiple Watch windows
Each works the same way
Just create an expression to be watched
Use Watchpoints instead of repeatedly typing the same expression in the Immediate window
Beware of setting too many Watchpoints – Execution will become quite slow

20. Setting WatchPoints (Illustration)
Watch the variable “f”

21. Other Debugging Windows (1)
The Autos window shows variables used in the current and previous statement

22. Other Debugging Windows (2)
The Locals window displays variables local to the current context

23. Other Debugging Windows (3)
Call stack shows the procedures and the order in which the procedures were called

24. Exceptions
Use to change the handling of exceptions when they occur