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Objectives

Tutorial 6 – Enhancing the Inventory Application Introducing Variables, Memory Concepts and Arithmetic.

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Objectives

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  1. Tutorial 6 – Enhancing the Inventory ApplicationIntroducing Variables, Memory Concepts and Arithmetic Outline6.1 Test-Driving the Enhanced Inventory Application6.2 Variables6.3 Handling the TextChanged Event6.4 Memory Concepts6.5 Arithmetic6.6 Using the Debugger: Breakpoints6.7 Internet and Web Resources6.8 Wrap-Up

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

  3. 6.1 Test-Driving the Enhanced Inventory Application

  4. 6.1 Test-Driving the Enhanced Inventory Application • Running the application Figure 6.1　Inventory application GUI displayed when the application is executed.

  5. 6.1 Test-Driving the Enhanced Inventory Application • Using the application • Enter data into the TextBoxes and click theCalculate TotalButton • Notice the result Figure 6.2　Running the Inventory application.

  6. Cleared output Label 6.1 Test-Driving the Enhanced Inventory Application • Notice the new feature • The output Label is cleared when new data is entered Figure 6.3　Modified Inventory application clears output Label after new input.

  7. 6.2 Variables • Adding code to the application • Declaring a variable • Keyword Dim • Data types • Built-in data type • Primitive data type

  8. Click event handler Variable declarations 6.2 Variables Figure 6.4　Declaring variables in event handler btnCalculate_Click.

  9. 6.2 Variables • Retrieving data from the user • Data is stored in the TextBox’s Text property • The Val function • Returns data type Double • Implicit conversion

  10. Assigning user input to variables 6.2 Variables Figure 6.5　Retrieving numerical input from TextBoxes.

  11. 6.2 Variables

  12. 6.2 Variables • Perform the multiplication • Displaying the result • Set the multiplication result to the Label’s Text property

  13. Calculating and displaying the result 6.2 Variables Figure 6.7　Multiplication, using variables in btnCalculate_Click.

  14. Result of calculation 6.2 Variables • Running the application • Enter data • Click the Calculate TotalButton • Notice the result Figure 6.8　Displaying the multiplication result using variables.

  15. 6.3 Handling the TextChanged Event • Create the event handler for the first TextBox • Double click the TextBox • TextChangedevent handler is created • Clearing the value • Use empty string • Repeat for second TextBox

  16. TextChanged event handler 6.3 Handling the TextChanged Event Figure 6.9　TextChanged event handler for Cartons per shipment:TextBox.

  17. 6.3 Handling the TextChanged Event Figure 6.10　TextChanged event handler for Items per carton:TextBox.

  18. Use keyword Dim to declare variables inside an event handler Assigning a property’s value to a variable Assigning a variable to a property Inventory.vb(1 of 2)

  19. Setting a TextBox’s Text property to an empty string Inventory.vb(2 of 2)

  20. 6.4 Memory Concepts • A simple variable • Corresponds to actual location in the computer’s memory • Name • Type • Size • Value Figure 6.12　Memory location showing name and value of variable intCartons. intCartons 12

  21. 10 12 6.4 Memory Concepts • Visualizing data • The value of each variable is stored in a separate memory location Figure 6.13　Memory locations after values for variables intCartons and intItems have been input. intCartons intItems

  22. 6.4 Memory Concepts • Using the variable’s data • Nondestructive when value is read from memory Figure 6.14　Memory locations after a multiplication operation. intCartons 12 intItems 10 120 intResult

  23. 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

  24. 6.5 Arithmetic

  25. 6.6 Using the Debugger: Breakpoints • Enable the debugger • Enabled by default • Change Solution ConfigurationComboBox to Debugif not enabled

  26. Solution Configuration ComboBox 6.6 Using the Debugger: Breakpoints Figure 6.16　Setting Solution Configuration to Debug.

  27. 6.6 Using the Debugger: Breakpoints • Methods of inserting breakpoints • Click inside the margin indicator bar • Right click the line of code and select 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

  28. Margin indicator bar Breakpoints 6.6 Using the Debugger: Breakpoints Figure 6.17　Setting two breakpoints.

  29. 6.6 Using the Debugger: Breakpoints • Run the application • Click the Calculate TotalButton Figure 6.18　Inventory application running.

  30. Title bar displays [break] 6.6 Using the Debugger: Breakpoints • The IDE title bar displays the application’s mode Figure 6.19　Title bar of the IDE displaying [break].

  31. 6.6 Using the Debugger: Breakpoints • Debugging the application • Program execution suspends at the first break point • Yellow arrow indicate next statement to execute

  32. Next executable statement Yellow arrow Breakpoints 6.6 Using the Debugger: Breakpoints Figure 6.20　Program execution suspended at the first breakpoint.

  33. 6.6 Using the Debugger: Breakpoints • To resume execution, select Debug > Continue • The application continues its normal execution • Quick Info box • Displays variable’s current value

  34. Quick Info box displays variable intResult’s value 6.6 Using the Debugger: Breakpoints Figure 6.21　Displaying a variable value by placing the mouse pointer over a variable name.

  35. 6.6 Using the Debugger: Breakpoints • Use the Debug > Continue command to complete the application • No more breakpoints, program will not suspend • The entire application executes to completion Figure 6.22　Program output.

  36. Disabled breakpoint 6.6 Using the Debugger: Breakpoints Figure 6.23　Disabled breakpoint.

  37. 6.6 Using the Debugger: Breakpoints • Disabling a breakpoint • Right click the line of code with the breakpoint • Select Disable Breakpoint • A hollow maroon circle indicates disabled breakpoint • Removing a breakpoint • Right click the line of code with the breakpoint • Select Remove Breakpoint • Or click the maroon circle in the margin indicator bar

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