CIS 115 Lecture 4

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.

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

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.

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

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)

Design the Interface – TOE Chart Task, Object, EventPlan the interface BEFORE creating in VBExamines all of the tasks involved in solutionTask (T) Object (O) Event (E)

Input Hours Worked Textbox, Label None

Input Pay Rate Textbox, Label None

Output Gross Pay Label (display), Label (title)

None

Calculate Gross Pay Button Click

Exit Program Button Click

Make a list of the controls needed Define values for each control's relevant properties:

Control Type Control Name TextForm (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"

Make a list the events/procedures needed Develop an algorithm for each procedure

Event Event Procedure Code AlgorithmbtnCalcGrossPay_Click Get hours worked from txtHoursWorked

Get hourly pay rate from txtPayRateMultiply hours worked by hourly pay rateAssign result to lblGrossPay

btnClose_Click End the application

Visualize the application running on the computer and design its user interface

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

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

LabelLabelLabel

Text Box Text Box

Label

2 Buttons

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 seeControl Type Control Name TextForm (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"

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

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

btnExit Button Click Event End

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

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

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

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