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### Microsoft Visual Basic 2005 BASICS

Lesson 6

Exponentiation, Order of Operations, and Error Handling

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

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

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

Order of Operations
• From your math classes
• 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

Order of Operations (cont.)

Microsoft Visual Basic 2005 BASICS

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

Order of Operations (cont.)

Microsoft Visual Basic 2005 BASICS

Order of Operations (cont.)

Microsoft Visual Basic 2005 BASICS

Order of Operations (cont.)

Microsoft Visual Basic 2005 BASICS

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

• 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

• 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

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

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

Handling Run-Time Errors (cont.)

Microsoft Visual Basic 2005 BASICS

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

• Error trapping
• Process of interrupting the normal chain of events and replacing that chain with your own code

Microsoft Visual Basic 2005 BASICS

Microsoft Visual Basic 2005 BASICS

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

Using MsgBox (cont.)

Microsoft Visual Basic 2005 BASICS

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

Using Exit Sub to Exit a Subroutine (cont.)

Microsoft Visual Basic 2005 BASICS

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

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

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

Summary (cont.)
• The MsgBoxfunction 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