Developing a Visual Basic Application

1. CIS 115 Lecture 4 Developing a Visual Basic Application

2. Problem • Create a Windows-based application that will calculate the Gross Pay earned for a worker, given the number of hours worked and hourly pay rate.

3. Step 1: Understand Problem • Clearly define the problem and identify what the program is to do • Purpose: To calculate a worker’s gross pay • Input: Number of hours worked, hourly pay rate • Process: Multiply number of hours worked by hourly pay rate (result is the user’s gross pay) • Output: Display a message indicating the user’s gross pay

4. Step 2: Design Solution Traditional Procedural Approach - Develop an algorithm: • Display message: "How many hours did you work?" • Allow user to enter number of hours worked • Store the number the user enters in memory • Display message: "How much are you paid per hour?" • Allow the user to enter an hourly pay rate • Store the number the user enters in memory • Multiply hours worked by pay rate and store the result in memory • Display a message with the result of the previous step This well-defined, ordered set of steps for solving a problem is called an algorithm.

5. Step 2: Design Solution (cont.) VB (GUI) Approach – Identify required controls and events/handlers • Inputs - entered into the program via Controls: • Hours Worked • Hourly Pay Rate • Processes - initiated by Events and carried out by the code contained in the corresponding Event Procedures: • Calculate Gross Pay • Gross Pay = hoursWorked * hourlyPayRate • Output - displayed to the user via Controls: • Gross Pay

6. Step 2: Design Solution (cont.) • Inputs (controls): • Hours Worked  Textbox, Label (title/prompt) • Hourly Pay Rate  Textbox, Label (title/prompt) • Processes (events/event procedures): • Calculate Gross Pay  Button(click) • Gross Pay = hoursWorked * hourlyPayRate • Exit Program  Button(click) • End • Outputs (controls): • Gross Pay Earned  Label (display result), Label (title)

7. Step 2: Design Solution (cont.) Design the Interface – TOE Chart • Task, Object, Event • Plan the interface BEFORE creating in VB • Examines all of the tasks involved in solution

8. Step 2: Design Solution (cont.) • Make a list of the controls needed • Define values for each control's relevant properties: Control TypeControl NameText Form (Default) "Wage Calculator" TextBox txtHoursWorked "" Label (Default) "Number of Hours Worked" TextBox txtPayRate "" Label (Default) "Hourly Pay Rate" Label lblGrossPay "$0.00" Label (Default) "Gross Pay Earned" Button btnCalcGrossPay "Calculate Gross Pay" Button btnExit “Exit"

9. Step 2: Design Solution (cont.) • Make a list the events/procedures needed • Develop an algorithm for each procedure EventEvent Procedure Code Algorithm btnCalcGrossPay_Click Get hours worked from txtHoursWorked Get hourly pay rate from txtPayRate Multiply hours worked by hourly pay rate Assign result to lblGrossPay btnClose_Click End the application

10. Step 2: Design Solution (cont.) • Visualize the application running on the computer and design its user interface

11. Step 3: Implementation • Creating the Visual Basic Application - Event Driven Programming Steps • Create the Interface / Window first • Input • Output • Set the Properties • Configure the appearance and behavior of the controls • Then Code the Application • Processes - Event Handing Methods

12. Step 3: Implementation(cont.) • Create the Interface - Use Visual Basic to create the forms and other controls identified in the previous step • This is the first use of Visual Basic, all of the previous steps have just been on paper • In this step you develop the portion of the application the user will see Label Text Box Label Text Box Label Label 2 Buttons

13. Step 3: Implementation(cont.) • Set Properties - Use Visual Basic to set properties for the forms and other controls from list you made earlier • In this step you still developing the portion of the application the user will see Control TypeControl NameText Form (Default) "Wage Calculator" TextBox txtHoursWorked "" Label (Default) "Number of Hours Worked" TextBox txtPayRate "" Label (Default) "Hourly Pay Rate" Label lblGrossPay "$0.00" Label (Default) "Gross Pay Earned" Button btnCalcGrossPay "Calculate Gross Pay" Button btnExit “Exit"

14. Step 3: Implementation(cont.) • Create the Events/Procedures - Use Visual Basic to create and write the code for the event procedures identified earlier • In this step you develop the methods behind the click event for each button • Unlike the interface, this portion of the application is invisible to the user

15. Step 3: Implementation(cont.) • btnCalculate • Button Click Event • Assignment statement • lblGrossPay.text = Val(txtHoursWorked.text) * Val(txtPayRate.text) • Gets data from txtHoursWorked.text and txtPayRate.text • Assigns results from hours * rate calculation to lblGrossPay.text • Val changes the text input from the text box into a number

16. Step 3: Implementation(cont.) • btnExit • Button Click Event • End

17. Step 4: Evaluation 3 Major Types of Errors • Syntax Errors – Language Errors • Caught by the Compiler & Interpreter • Visual Basic – wavy line under problem code • Run-Time Errors • Program will not run to normal completion • Program Crashes • Logic Errors • Program Runs but produces incorrect results

18. Step 4: Evaluation(cont.) • Attempt to run the application - find syntax errors and runtime errors • Correct any syntax errors found – indicated by wavy blue line • All syntax errors must be removed before Visual Basic will create a program that actually runs • Find and correct and correct any runtime errors until program runs to normal completion

19. Step 4: Evaluation(cont.) • Run the application using test data as input • Run the program with a variety of test data • Must test for expected and unexpected input • negative numbers, blank text box, etc. • will talk about how to deal with invalid input later • Check the results to be sure that they are correct • Correct any logic errors found • Repeat this step as many times as necessary

20. Homework • Homework 2 • Visual Basic Application • See handout for details and due date • Questions?