Microsoft Visual Basic 2005 BASICS Lesson 6 Exponentiation

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

Objectives n n 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 2

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

Exponentiation n Exponentiation ¡ ¡ n 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 4

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

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

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

Order of Operations (cont. ) 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

Using the Visible Property to Enhance Output n Visible property ¡ n 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 11

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

Using Comments n Use an apostrophe to create comments. ¡ n 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 13

Using Comments (cont. ) n Use comments to (cont. ) ¡ ¡ n 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 14

Handling Run-Time Errors n Exceptions or run-time errors ¡ n 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 15

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

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

Trapping Run-Time Errors with the Try/Catch Structure n Write code that will execute when a runtime error occurs. ¡ ¡ n 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 18

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

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

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

Using Msg. Box (cont. ) Microsoft Visual Basic 2005 BASICS 22

Using Exit Sub to Exit a Subroutine n The Exit Sub statement ¡ Forces the event procedure to end n ¡ ¡ Regardless of whethere 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 23

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

Summary n n n 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 25

Summary (cont. ) n n 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 26

Summary (cont. ) n 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 27

Summary (cont. ) n n The Msg. Box 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 28