Fundamentals of Programming in VB: Examples
List Box Example
The following example shows the VB codes, its design view, and run-time results
of using a listbox, where results of math calculations are added t othe list box
line by line.
Private Sub btnCompute_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnCompute.Click
lstResults.Items.Clear()
lstResults.Items.Add(3 + 2)
lstResults.Items.Add(3 - 2)
lstResults.Items.Add(3 * 2)
lstResults.Items.Add(3 / 2)
lstResults.Items.Add(3 ^ 2)
lstResults.Items.Add(2 * (3 + 4))
End Sub
Declaring and Assigning Numerical Variables Using a List Box
The example below shows how variables are declared. The screen shows the
results before and after clicking the button.
Private Sub btnCompute_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnCompute.Click
Dim a As Double
Dim b As Double = 3
lstResults.Items.Clear()
lstResults.Items.Add(a)
lstResults.Items.Add(b)
a = 5
lstResults.Items.Add(a * (2 + b))
End Sub
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Fundamentals of Programming in VB: Examples
Built-in Math Function and List Box
The following codes show the use of some Math functions. It also shows how the use of “
With…..End With” block in a List Box can reduce the amount of repeated typing.
Private Sub btnCompute_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnCompute.Click
Dim n As Double
Dim root As Double
n = 6.76
root = Math.Sqrt(n)
With lstResults.Items
.Clear()
.Add(root)
.Add(Int(n))
.Add(Math.Round(n, 1))
End With
End Sub
Use of String Variables in a List Box
The screens show the results before and after clicking the button.
Private Sub btnDisplay_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnDisplay.Click
Dim today As String
today = "Monday"
With lstOutput.Items
.Clear()
.Add("today")
.Add(today)
End With
End Sub
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Fundamentals of Programming in VB: Examples
Concatenation of Strings as variables
The following codes show how two strings declared as variables can be joined
together. The screen displays the result upon clicking on the button.
Private Sub btnDisplay_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnDisplay.Click
Dim quote1, quote2, quote As String
quote1 = "The ballgame isn't over, "
quote2 = "until it's over."
quote = quote1 & quote2
txtOutput.Text = quote & "
Yogi Berra"
End Sub
Reading from and Writing to Text Boxes
The following code reads data as text from two text boxes and converts into a
number and then adds and places the result in another text box.
Private Sub btnCompute_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnCompute.Click
Dim num1, num2, sum As Double
num1 = CDbl(txtFirstNum.Text)
num2 = CDbl(txtSecondNum.Text)
sum = num1 + num2
txtSum.Text = CStr(sum)
End Sub
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Fundamentals of Programming in VB: Examples
Use of IndexOf, Substring, and Length Properties of a String
The following program parses a name consisting of two parts, finds the position
of an empty string, determines the parts of the name, and then finds the number
of characters in the last part of the name.
Private Sub btnAnalyze_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnAnalyze.Click
Dim fullName, firstName, lastName As String
Dim n As Integer
fullName = txtName.Text
n = fullName.IndexOf(" ")
firstName = fullName.Substring(0, n)
lastName = fullName.Substring(n + 1)
With lstResults.Items
.Clear()
.Add("First name: " & firstName)
.Add("Your last name has " & lastName.Length & " letters.")
End With
End Sub
Using Properties and Methods of a Text Box
The following codes show how to enable and disable a text box, change color, and
bring focus on a text box.
Private Sub btnDisable_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnDisable.Click
txtBox.Enabled = False
txtBox.BackColor = Color.BurlyWood
End Sub
Private Sub btnEnable_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnEnable.Click
txtBox.Enabled = True
txtBox.Focus()
End Sub
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Fundamentals of Programming in VB: Examples
Using the Editor to Automatically Locate a Property of a Control such as Text Box
and also the Correct Assignments
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Fundamentals of Programming in VB: Examples
Using Properties such as Background Color of a Text Box
The following codes show how properties of text box such as background color of a text
box can be changed. As shown, all code sections are fired when Enter event of a text
box is executed.
Private Sub txtGreen_Enter(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles txtGreen.Enter
txtGreen.BackColor = Color.Green
txtYellow.BackColor = Color.DarkGray
txtRed.BackColor = Color.DarkGray
End Sub
Private Sub txtYellow_Enter(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles txtYellow.Enter
txtGreen.BackColor = Color.DarkGray
txtYellow.BackColor = Color.Yellow
txtRed.BackColor = Color.DarkGray
End Sub
Private Sub txtRed_Enter(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles txtRed.Enter
txtGreen.BackColor = Color.DarkGray
txtYellow.BackColor = Color.DarkGray
txtRed.BackColor = Color.Red
End Sub
Problem: A motorist starts his car with a full tank of gas (14.1 gallons) and with a
odometer reading of 23,340 miles. He stops to fill the tank again at an odometer
reading of 23,695 miles. How many miles per gallon did he get in his car? Write your
answer in a list box.
Private Sub btnCompute_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnCompute.Click
Dim miles, gallonsUsed, milesPerGallon As Double
miles = 23695 - 23340
gallonsUsed = 14.1
milesPerGallon = Math.Round(miles/gallonsUsed)
lstOutput.Items.Add(milesPerGallon)
End Sub
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Fundamentals of Programming in VB: Examples
Problem: It is found in a survey that Americans use an average of 1600 gallons of
water per person per day, including industrial use. How many gallons of water
are used each year in the United States?
Private Sub btnCompute_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnCompute.Click
Dim waterPerPersonPerDay, people, days, waterUsed As Double
waterPerPersonPerDay = 1600
people = 300000000
days = 365
waterUsed = waterPerPersonPerDay * people * days
lstOutput.Items.Add(waterUsed)
End Sub
Problem: Write a program to request the name of baseball team, the number of
games won, and the number of games lost as input, and then display the name
of the team and the percentage of games won.
Private Sub btnCompute_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnCompute.Click
Dim numberOfGames As Integer
Dim percent, percentage As Double
numberOfGames = CInt(txtWon.Text) + CInt(txtLost.Text)
percent = CDbl(txtWon.Text) / numberOfGames
percentage = 100 * Math.Round(percent, 5)
txtPercent.Text = txtTeam.Text & " won " & percentage & " percent of its
games."
End Sub
Note the highlighted code for rounding the percent upto three decimals only.
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