Visual Basic 'NET BASICS

1
Visual Basic .NET BASICS

• Lesson 5
• Exponentiation, Order of Operations, and Error
  Handling

2
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.

3
Objectives (continued)

• Handle run-time errors using the Try/Catch
  structure.
• Display messages using the MsgBox function.
• Control program flow using the Exit Sub
  statement.

4
Exponentiation

• Exponentiation is the process of raising a number
  to a power.
• The symbol that represents exponentiation is the
  caret ().
• The operator raises the number to the left of the
  operator to the power that appears on the right
  of the operator.

5
Order of Operations

• From your math classes, you may recall the rules
  called the order of operations.
• Visual Basic .NET uses the same set of rules for
  its calculations.
• Visual Basic .NET allows you to use parentheses
  to override the order of operations.

6
Using the Visible Property to Enhance Output

• You have used the Visible property to make an
  image appear and disappear.
• Another example of a useful application of the
  Visible property is preventing labels from
  appearing until you are ready for the user to see
  the label.
• By initially setting the Visible property to
  False, the output will remain invisible until you
  make the labels visible in the code.

7
Using Comments

• The Properties window allows you to easily alter
  the properties of objects.
• Two of the most important properties of a form
  are the Text and Name properties.
• The Text property specifies the text that appears
  in the title bar.
• The Name property names the object for coding.

8
Handling Run-Time Errors

• Users will enter all kinds of unexpected data or
  fail to enter required data.
• These are exceptions or run-time errors.
• Run-time errors are not detected at the time the
  program is compiled because the error is caused
  by conditions that do not exist until the program
  is running.
• When a run-time error occurs, the system throws
  an exception.

9
Trapping Run-Time Errors with the Try/Catch
Structure

• Visual Basic .NET allows you to write code that
  will executed when a run-time error occurs.
• To specify what code will execute when an error
  occurs, you must turn on error trapping.
• To turn on error trapping, place a Try statement
  above the code that may generate a run-time
  error.
• The code that will be executed if an error occurs
  is often called an error handler.

10
Using MsgBox

• One of the easiest ways to display a message of
  your own, such as an error message, is to use the
  MsgBox function.
• The MsgBox function causes a dialog box to pop
  up, displaying a message that you specify.

11
Using End 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.
• The procedure will end when the flow of execution
  reaches the Exit Sub statement and can be placed
  anywhere in the subroutine.
• This allows the programmer to exit the subroutine
  for different reasons.

12
Summary

• The exponential operator () raises a number to a
  power.
• The rules that dictate the order that math
  operators are applied in a formula are called the
  order of operations.
• Parentheses can be used to override the order of
  operations.
• The Visible property can be used to hide a label
  until you are ready for the user to see it.

13
Summary (continued)

• The apostrophe is used to add comments to Visual
  Basic. NET code. Comments allow you to keep track
  of changes in code and explain the purpose of
  code. Comments are often called internal
  documentation.
• Errors that occur while a program is running are
  called run-time errors or exceptions. Visual
  Basic. NET allows you to trap errors, using
  Try/Catch, and execute special code that you
  specify to handle the error.

14
Summary (continued)

• The MsgBox function pops up a dialog box,
  delivering a message to the user.
• When you detect errors that cannot be completely
  handled, you should send the user a message and
  use the Exit Sub to end the event procedure
  before the error can cause additional problems.