1. Microsoft Visual Basic 2005 BASICSyo
Microsoft Visual Basic 2005 BASICS
Lesson 6
Exponentiation, Order of Operations, and Error Handling

2. yo
Objectives
Use the exponentiation operator to raise numbers to a power.
Describe the order of operations.
Use the Visible property to enhance output.
Describe the purpose of comments in programs.
Microsoft Visual Basic 2005 BASICS

3. yo
Objectives (cont.)
Handle run-time errors using the Try/Catch structure.
Display messages using the MsgBox function.
Control program flow using the Exit Sub statement.
Microsoft Visual Basic 2005 BASICS

4. Exponentiation Exponentiationyo
Exponentiation
Exponentiation
Process of raising a number to a power
Represented by the caret (^)
Operator raises the number to the left of the operator to the power that appears on the right of the operator
Microsoft Visual Basic 2005 BASICS

5. Order of Operations From your math classes Visual Basic Parentheses
Recall the rules called the order of operations
Visual Basic
Uses the same set of rules for its calculations
Parentheses
Override the order of operations
Microsoft Visual Basic 2005 BASICS

6. Order of Operations (cont.)
Microsoft Visual Basic 2005 BASICS

7. Order of Operations (cont.)yo
Order of Operations (cont.)
Basic order of operations
Exponentiation
Unary plus and minus
Multiplication, division, integer division, modulus
Addition and subtraction
Microsoft Visual Basic 2005 BASICS

8. Order of Operations (cont.)
Microsoft Visual Basic 2005 BASICS

9. Order of Operations (cont.)
Microsoft Visual Basic 2005 BASICS

10. Order of Operations (cont.)
Microsoft Visual Basic 2005 BASICS

11. Using the Visible Property to Enhance Outputyo
Using the Visible Property to Enhance Output
Visible property
Prevents labels from appearing until you are ready for the user to see the label
By initially setting the Visible property to False
Output will remain invisible until you make the labels visible in the code
Microsoft Visual Basic 2005 BASICS

12. Using the Visible Property to Enhance Output (cont.)
Microsoft Visual Basic 2005 BASICS

13. Using Comments Use an apostrophe to create comments. Use comments toyo
Using Comments
Use an apostrophe to create comments.
Comments can appear on their own lines.
Use comments to
Explain the purpose of a program
Keep notes regarding changes to the source code
Store the names of programmers for future reference
Microsoft Visual Basic 2005 BASICS

14. Using Comments (cont.) Use comments to (cont.)yo
Using Comments (cont.)
Use comments to (cont.)
Explain the parts of your program
Temporarily remove lines from the program during testing
Comments added to programs are often called internal documentation.
Microsoft Visual Basic 2005 BASICS

15. Handling Run-Time Errorsyo
Handling Run-Time Errors
Exceptions or run-time errors
Errors that occur when the program is running
Run-time errors are not detected at the time the program is compiled.
Microsoft Visual Basic 2005 BASICS

16. Handling Run-Time Errors (cont.)
When a run-time error occurs
The system throws an exception.
A signal is sent to the program that needs to be handled or caught.
Microsoft Visual Basic 2005 BASICS

17. Handling Run-Time Errors (cont.)
Microsoft Visual Basic 2005 BASICS

18. Trapping Run-Time Errors with the Try/Catch Structureyo
Trapping Run-Time Errors with the Try/Catch Structure
Write code that will execute when a run-time error occurs.
You must turn on error trapping.
Place a Try statement above the code that may generate a run-time error.
Code is often called an error handler.
Microsoft Visual Basic 2005 BASICS

19. Trapping Run-Time Errors with the Try/Catch Structure (cont.)
Error trapping
Process of interrupting the normal chain of events and replacing that chain with your own code
Microsoft Visual Basic 2005 BASICS

20. Trapping Run-Time Errors with the Try/Catch Structure (cont.)
Microsoft Visual Basic 2005 BASICS

21. Using MsgBox MsgBox functionyo
Using MsgBox
MsgBox function
One of the easiest ways to display a message of your own
Such as an error message
Causes a dialog box to pop up
Displays a message that you specify
Microsoft Visual Basic 2005 BASICS

22. Using MsgBox (cont.)
Microsoft Visual Basic 2005 BASICS

23. Using Exit Sub to Exit a Subroutineyo
Using Exit Sub to Exit a Subroutine
The Exit Sub statement
Forces the event procedure to end
Regardless of whether there is more code in the procedure
Can be placed anywhere in the subroutine
Allows the programmer to exit the subroutine for different reasons
Microsoft Visual Basic 2005 BASICS

24. Using Exit Sub to Exit a Subroutine (cont.)
Microsoft Visual Basic 2005 BASICS

25. Summary The exponential operator (^) raises a number to a power.yo
Summary
The exponential operator (^) raises a number to a power.
The rules that dictate the order in which math operators are applied in a formula are called the order of operations.
Parentheses can be used to override the order of operations.
Microsoft Visual Basic 2005 BASICS

26. Summary (cont.)
The Visible property can be used to hide a label until you are ready for the user to see it.
The apostrophe is used to add comments to Visual Basic code. Comments allow you to keep track of changes and to explain the purpose of code. Comments are often called internal documentation.
Microsoft Visual Basic 2005 BASICS

27. yo
Summary (cont.)
Errors that occur while a program is running are called run-time errors or exceptions.
Visual Basic allows you to trap errors, using Try/Catch, and execute special code that you specify to handle the error.
Microsoft Visual Basic 2005 BASICS

28. Summary (cont.)
The MsgBox function pops up a dialog box, delivering a message to the user.
When you detect errors that cannot be handled completely, send the user a message and use an Exit Sub statement to end the event procedure before the error can cause additional problems.
Microsoft Visual Basic 2005 BASICS