Mgmt 362a Enhancing the Inventory Application

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• Mgmt 362a Enhancing the Inventory Application
• Introducing Variables, Memory Concepts and
  Arithmetic

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Outline

• 6.1 Test-Driving the Enhanced Inventory
  Application
• 6.2 Variables
• 6.3 Handling the TextChanged Event
• 6.4 Memory Concepts
• 6.5 Arithmetic
• 6.6 Using the Debugger Breakpoints
• 6.7 Internet and Web Resources
• 6.8 Wrap-Up

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Objectives

• In this tutorial you will learn
• Create variables.
• Handle the TextChanged event.
• Apply basic memory concepts using variables.
• Use the precedence rules of arithmetic operators.
• Set breakpoints to debug applications.

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6.1 Test-Driving the Enhanced Inventory
Application

• The inventory manager notices a flaw in your
  Inventory application. Although the application
  calculates the correct result, that result
  continues to display even after new data is
  entered. The only timethe output changes is when
  the inventory manager clicks theCalculate Button
  again. You need to alter the Inventory
  applicationto clear the result as soon as the
  user enters new information intoeither of the
  TextBoxes, to avoid any confusion over the
  accuracy of your calculated result.

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6.1 Test-Driving the Enhanced Inventory
Application (Cont.)

• Figure 6.1 Inventory application GUI displayed
  when the application runs.

Running the application
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6.1 Test-Driving the Enhanced Inventory
Application (Cont.)

• Figure 6.2 Running the Inventory application.

• Using the application
• Enter data into the TextBoxes and click the
  Calculate Total Button
• Notice the result

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6.1 Test-Driving the Enhanced Inventory
Application (Cont.)

• Figure 6.3 Enhanced Inventory application
  clears output Label after new input.

• Notice the new feature
• The output Label is cleared when new data is
  entered

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6.2 Variables

• Adding code to the application
• Declaring a variable
• Keyword Dim
• Data types
• Built-in data type
• Primitive data type

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Good Programming Practice

• Typically, variable-name identifiers begin witha
  lowercase letter. Every word in the name
  afterthe first word should begin with a capital
  letter,for example, firstNumber.

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Good Programming Practice

• Use only letters and digits as characters
  foryour variable names.

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6.2 Using Variables in the Inventory Application

• Figure 6.4 Declaring variables in event handler
  calculateButton_Click.

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6.2 Using Variables in the Inventory Application
(Cont.)

• Retrieving data from the user
• Data is stored in the TextBoxs Text property
• The Val function
• Returns data type Double
• Implicit conversion

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6.2 Using Variables in the Inventory Application
(Cont.)

• Figure 6.5 Retrieving numerical input from
  TextBoxes.

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6.2 Using Variables in the Inventory Application
(Cont.)

• Figure 6.6 Visual Basic built-in data types.

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6.2 Using Variables in the Inventory Application
(Cont.)

• Perform the multiplication
• Displaying the result
• Set the multiplication result to the Labels Text
  property

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6.2 Using Variables in the Inventory Application
(Cont.)

• Figure 6.7 Multiplication, using variables in
  calculateButton_Click.

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6.2 Using Variables in the Inventory Application
(Cont.)

• Figure 6.8 Displaying the multiplication result
  using variables.

• Running the application
• Enter data
• Click the Calculate Total Button
• Notice the result

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6.3 Handling the TextChanged Event

• Create the event handler for the first TextBox
• Double click the TextBox
• TextChanged event handler is created
• Clearing the value
• Use empty string
• Repeat for second TextBox

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6.3 Handling the TextChanged Event (Cont.)

• Figure 6.9 TextChanged event handler for
  Cartons per shipment TextBox.

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Good Programming Practice

• If a statement is wider than the code editor
  window, use the line-continuation character
  within the statement to continue it on the next
  line.

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6.3 Handling the TextChanged Event (Cont.)

• Figure 6.10 TextChanged event handler for Items
  per carton TextBox.

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Outline
(1 of 2 )
Use keyword Dim to declare variables inside an
event handler
Assigning a propertys valueto a variable
Assigning a variableto a property
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Outline
(2 of 2 )
Setting a TextBoxs Text property to an empty
string
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6.4 Memory Concepts

• Figure 6.12 Memory location showing name and
  value of variable cartons.

• A simple variable
• Corresponds to actual location in the computers
  memory
• Name
• Type
• Size
• Value

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6.4 Memory Concepts (Cont.)

• Figure 6.13 Memory locations after values for
  variables cartons anditems have been input.

• Visualizing data
• The value of each variable is stored in a
  separate memory location

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6.4 Memory Concepts (Cont.)

• Figure 6.14 Memory locations after a
  multiplication operation.

• Using the variables data
• Nondestructive when value is read from memory

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6.5 Arithmetic

• Operator precedence
• Operators in expressions contained within a pair
  of parentheses are evaluated first
• Exponentiation is applied next
• Unary positive and negative are applied
• Multiplication and floating-point division
  operations
• Division is applied
• Modulus operations are second to last
• Lastly, Addition and subtraction operations

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6.5 Arithmetic (Cont.)
Figure 6.15 Arithmetic operators.
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Common Programming Error

• Attempting to divide by zero is a runtime
  error(that is, an error that has its effect
  while the application executes). Dividing by
  zeroterminates an application.

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Good Programming Practice

• Using redundant parentheses in complex arithmetic
  expressions can make the expressions easier to
  read.

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6.6 Using the Debugger Breakpoints

• Methods of inserting breakpoints
• Click inside the margin indicator bar
• Right click the line of code and select
  Breakpoint gt Insert Breakpoint
• Breakpoints
• You can set as many as you like
• Solid maroon circle appears for each breakpoint
• Can be set during design more, break mode, or run
  mode

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6.6 Using the Debugger Breakpoints (Cont.)

• Figure 6.16 Setting two breakpoints.

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6.6 Using the Debugger Breakpoints (Cont.)

• Figure 6.17 Inventory application running.

Run the application Click the Calculate Total
Button
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6.6 Using the Debugger Breakpoints (Cont.)

• Figure 6.18 Title bar of the IDE displaying
  (Debugging).

The IDE title bar displays the applications mode
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6.6 Using the Debugger Breakpoints (Cont.)

• Debugging the application
• Program execution suspends at the first break
  point
• Yellow arrow indicate next statement to execute

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6.6 Using the Debugger Breakpoints (Cont.)

• Figure 6.19 Application execution suspended at
  the first breakpoint.

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6.6 Using the Debugger Breakpoints (Cont.)

• To resume execution, select Debug gt Continue
• The application continues its normal execution
• Quick Info box
• Displays variables current value

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6.6 Using the Debugger Breakpoints (Cont.)

• Figure 6.20 Displaying a variable value by
  placing the mouse pointer overa variable name.

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6.6 Using the Debugger Breakpoints (Cont.)

• Figure 6.21 Application output.

• Use the Debug gt Continue command to complete the
  application
• No more breakpoints, program will not suspend
• The entire application executes to completion

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6.6 Using the Debugger Breakpoints (Cont.)

• Disabling a breakpoint
• Right click the line of code with the breakpoint
• Select Breakpoint gt Disable Breakpoint
• A hollow maroon circle indicates disabled
  breakpoint

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6.6 Using the Debugger Breakpoints (Cont.)

• Figure 6.22 Disabled breakpoint.

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6.6 Using the Debugger Breakpoints (Cont.)

• Removing a breakpoint
• Right click the line of code with the breakpoint
• Select Breakpoint gt Remove Breakpoint
• Or click the maroon circle in the margin
  indicator bar