Debugging
Visual Basic provides many tools to help analyze how your code operates. These
debugging tools are particularly useful in locating the source of errors, or
bugs. You can also use them to help you learn how code written
by other people works. When you write your code, you will never be able to create
code that works first time round perfectly. Or if you do, if you change another
section of code, this may well affect code you have already written which then
does not work. There are generally three types of errors:
Run Time Errors
These occur while your application is running, when Visual Basic finds a statement
that is impossible to carry out, such as multiplying the contents of TextBox1
by 10 when textbox1 contains 'Hello'. If this error occurs when running Visual
Basic, a dialog is displayed like the one below. You are given the error number
along with its message. You have the option to End the current program, Debug
the program which pauses the code, or to get help on that error
Visual Basic Error Dialog Box
If however an error occurs once your application has been made into an exe,
the error number and message are given. But once the OK button has been pressed,
the program closes.
Language Errors
These result from incorrectly structured code. For example, having an Do statement
without a corresponding Loop statement, or an opening quote for a string, but
no closing one. These sorts of errors are picked out, either the moment you
leave the line in the case of the missing quotes, or just before the code executes
in the case of the Do...Loop example.
Logic Errors
These errors occur when the code you have written does not run the way you
expected it. No error message is given as the code is using the correct syntax,
and is not performing invalid operations, however it is not giving the expected
result. This is by far the hardest error to track down. Only by going through
your code very methodically and analysing your results will you be able to find
the cause (or by very good luck, but don't rely on it!)