1. How to Debug VB .NET Code

2. Types of Error
Programming errors are generally broken down into three types:
Design-time,
Runtime,
and Logic errors.

3. Design-time error
Also known as a syntax error. These occur when the environment you're programming in doesn't understand your code.
These are easy to track down in VB.NET, because you get a blue wiggly line pointing them out.
If you try to run the program, you’ll get a dialogue box popping up telling you that there were Build errors.

4. Runtime errors
A lot harder to track down. As their name suggests, these errors occur when the program is running. They happen when your program tries to do something it shouldn’t be doing. An example is trying to divide by zero.
Runtime errors usually cause your program to crash. If and when that happens, you get the blame. After all, you’re the programmer, and you should write code to trap runtime errors.

5. Logic errors
Also occur when the program is running. They happen when your code doesn’t quite behave the way you thought it would.
A classic example is creating an infinite loop of the type “Do While x is greater than 10”. If x is always going to be greater than 10, then the loop has no way to exit, and just keeps going round and round.
Logic errors tend not to crash your program. But they will ensure that it doesn’t work properly.

6. Logic errors
There will be no wiggly lines and therefore no Build errors.
Also, no runtime exception will crash the program.
So how to find out where is the logical error?
Here comes the debugger job.

7. Breakpoints Another weapon in your debugging armory is the Breakpoint.
A breakpoint is like a note to VB.NET to stop your program at a particular place. You add one to your code by clicking in the margins.
A brown circled then appears, indicating where the code will break.
The following two images show how to add one:

8. Breakpoints
Run your program again. You are immediately returned to the coding window.
The place where you put the breakpoint will now have a yellow arrow on top of the brown circle.
The brown highlighted line will now be yellow

9. Breakpoints
The yellow highlight indicates where in your code VB.NET is.
To continue checking
your code, press F10 on your keyboard (you can also press F11, but this will jump into any Subs or Functions you’ve set up.)
The next line in your code will be highlighted:

10. Breakpoints
The yellow arrow, and the yellow highlight, jump down one line. Press the F10 key again.
Then hold you mouse of the letter variable.
The value this variable currently holds will be displayed:

11. Breakpoints
You can continue pressing the F10 key until you’ve spotted the error. Or you can use
another debugging tool – the Locals window.
While your program is still in Debug mode (the yellow line will still be there, if it is), click Debug > Windows > Locals from the menu bar.
You should see the following in the bottom left of your screen:
Locals means “Local variables”. That is, variables declared in this section of the code.

12. Commenting your code
In some cases you need to comment out a whole block of code.
To do so, highlight it first. Then click the comment icon on the toolbar:
The icon next to it removes the comments from highlighted code.