Visual Basic Programming Tutorial: Functions, Loops, Arrays, and File Operations

Posted on May 6, 2024 in Technology

Code

Imports System.Drawing.Printing

Public Class Form1

 Dim pSize As PaperSize

 Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles

MyBase.Load

 Dim InstPrinters As String

 ‘ Find all printers installed

 For Each InstPrinters In _

 PrinterSettings.InstalledPrinters

 cboPrinters.Items.Add(InstPrinters)

 Next InstPrinters

 ‘ Set the combo to the first printer in the list

 cboPrinters.SelectedIndex = 0

 ‘ Put the available paper sizes in a combo box for the user to select

 For i = 0 To PrintDocument1.PrinterSettings.PaperSizes.Count – 1

 pSize = PrintDocument1.PrinterSettings.PaperSizes.Item(i)

 cboPaperSize.Items.Add(pSize)

 Next

 End Sub

 Private Sub btnPrintPreview_Click(ByVal sender As System.Object, ByVal e As

System.EventArgs) Handles btnPrintPreview.Click

 PrintPreviewDialog1.Document = PrintDocument1

 PrintPreviewDialog1.ShowDialog()

 End Sub

 Private Sub PrintDocument1_PrintPage(ByVal sender As System.Object, ByVal e As

System.Drawing.Printing.PrintPageEventArgs) Handles PrintDocument1.PrintPage

 Dim grtext As Graphics = e.Graphics ‘Declars grtext as a graphics object capable of

printing both text and graphics

 Dim font As New Font(“Courier New”, 12, FontStyle.Italic) ‘Define a font that we can

use later

 ‘Now we tell the program what we want to be printed in PrintDocument1

 grtext.DrawString(txtToPrint.Text, Me.Font, Brushes.Black, 100, 150) ‘Uses the forms

Font.

 grtext.DrawString(txtToPrint.Text, font, Brushes.Red, 100, 300) ‘ Uses the font we made

 grtext.DrawString(“This is a test page”, Me.Font, Brushes.Brown, 100, 350)

 End Sub

 Private Sub btnPrint_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)

Handles btnPrint.Click

 PrintDocument1.PrinterSettings.PrinterName = cboPrinters.Text ‘Set the printer name

to the selected printer

 PrintDocument1.DefaultPageSettings.PaperSize = pSize ‘set the paper size to

what the user selected

 ‘PrintDocument1.DefaultPageSettings.PaperSize =

PrintDocument1.PrinterSettings.PaperSizes.Item(0)

 PrintDocument1.Print()

 End Sub

End Class

Function convert to C

Function FtoC(ByVal t As Double) As Double
 ‘Convert Fahrenheit temperature to Celsius
 Dim C As Double
 C = (5 / 9) * (t – 32)
 Return C
 End Function
Now we can use the function in another subroutine
 Private Sub btnConvert_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
Handles btnConvert.Click
 Dim Celsius, Fahrenheit As Double
 Fahrenheit = CDbl(txtTempF.Text)
 Celsius = FtoC(Fahrenheit)
 txtTempC.Text = CStr(Celsius)
 End Sub

Do-Until loops

Private Sub btnConvert_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnConvert.Click    Dim num As Integer    num = 6 
    txtResult.Clear() 
 
    Do 
      txtResult.AppendText(CStr(num) & vbCrLf) 
      num = num + 1    Loop Until num <= 7 
 
  End Sub 
 

Subroutines

Private Sub btnConvert_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnConvert.Click 
 
    Dim x, y As Double x and y are changed by GetNumbers so that DisplaySum can use the    GetNumbers(x, y) 
    DisplaySum(x, y) updated values 
  End Sub 
    
    Sub GetNumbers(ByRef x As Double, ByRef y As Double) 
    ‘Get the numbers from the textboxes and store as x and y 
     x = CDbl(txtX.Text)    y = CDbl(txtY.Text) 
 
  End Sub 
    Sub DisplaySum(ByVal x As Double, ByVal y As Double) 
    Dim sum As Double    sum = x + y 
    txtResult.Text = CStr(sum) 
 
  End Sub 

For next loop


Private Sub btnConvert_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnConvert.Click 
    Dim i As Integer 

    txtResult.Clear()    For i = 1 To 5 Step 1      txtResult.AppendText(CStr(i * 2) & vbCrLf)    Next  End Sub
  
 

Array

Dim students(29) As String
If we don’t say how many elements are in the array we can do that later using the ReDim command.
  Dim students() As String
  Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
Handles Button1.Click
    ReDim students(4)
    students = {“Dave”, “John”, “Betty”, “Steve”, “Matthew”}
ReDim Preserve

end sub

Searching for an element in an array

Array.IndexOf(arrayName, value)  – returns the index of the first occurance of value in arrayName.

Function Returns an Array

eg. Function GetGrades(ByVal numGrades As Integer) As Double() 
 
This function returns an array of doubles. The function is sent a single integer. 
 
Manually Finding the Maximum 
 
  Dim students(6) As String 
 
  Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnGenList.Click 
 
    Dim max As String 
    Dim numStudents As Integer 
 
    students = {“Dave”, “John”, “Betty”, “Steve”, “Matthew”, “Aaron”, “Patricia”}    numStudents = students.Count 
 
    lstStudents.Items.Clear() 
 
    max = students(0) 
 
    For i As Integer = 1 To (numStudents – 1) 
      If students(i) > max Then 
        max = students(i) 
      End If 
    Next 
 
    lstStudents.Items.Add(max) 
 
  End Sub 
 

Performing a Manual Sort

Dim students(6) As String 
 
  Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnGenList.Click 
 
    Dim temp1 As String 
    Dim count As Integer = 0 
    Dim numStudents As Integer 
 
    students = {“Dave”, “John”, “Betty”, “Steve”, “Matthew”, “Aaron”, “Patricia”}    numStudents = students.Count 
 
    lstStudents.Items.Clear() 
    ‘ListBox1.Items.Add(CStr(numStudents)) 
 
 
    For j As Integer = 1 To (numStudents – 1) 
      For i As Integer = 1 To (numStudents – 1 – count) 
        If students(i) < students(i – 1) Then 
          temp1 = students(i – 1)
          students(i – 1) = students(i) 
          students(i) = temp1 
        End If 
      Next 
      count = count + 1 
    Next 
 
 
    For i As Integer = 0 To (numStudents – 1) 
      ‘Array.Sort(students) 
      lstStudents.Items.Add(students(i)) 
    Next 
 
  End Sub 
 
Reading a File directly into a List Box

In the following example we open a file (I chose a file called Months.txt) and display the resutls in a
list box.
 Private Sub OpenToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles OpenToolStripMenuItem.Click
 Dim textfile As String
 OpenFileDialog1.Filter = “All Files (*.*) | *.* | Text Files (*.txt) | *.txt”
 OpenFileDialog1.ShowDialog()
 textfile = OpenFileDialog1.FileName
 lstDisplay.DataSource = IO.File.ReadAllLines(textfile)
 lstDisplay.SelectedItem = Nothing
 End Sub 
 

reading

Dim students(6) As String 
 
  Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnGenList.Click 
 
    Dim temp1 As String 
    Dim count As Integer = 0 
    Dim numStudents As Integer 
 
    students = {“Dave”, “John”, “Betty”, “Steve”, “Matthew”, “Aaron”, “Patricia”}    numStudents = students.Count 
 
    lstStudents.Items.Clear() 
    ‘ListBox1.Items.Add(CStr(numStudents)) 
 
 
    For j As Integer = 1 To (numStudents – 1) 
      For i As Integer = 1 To (numStudents – 1 – count) 
        If students(i) < students(i – 1) Then 
          temp1 = students(i – 1)
          students(i – 1) = students(i) 
          students(i) = temp1 
        End If 
      Next 
      count = count + 1 
    Next 
 
 
    For i As Integer = 0 To (numStudents – 1) 
      ‘Array.Sort(students) 
      lstStudents.Items.Add(students(i)) 
    Next 
 
  End Sub 
 
Reading a File directly into a List Box

In the following example we open a file (I chose a file called Months.txt) and display the resutls in a
list box.
 Private Sub OpenToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles OpenToolStripMenuItem.Click
 Dim textfile As String
 OpenFileDialog1.Filter = “All Files (*.*) | *.* | Text Files (*.txt) | *.txt”
 OpenFileDialog1.ShowDialog()
 textfile = OpenFileDialog1.FileName
 lstDisplay.DataSource = IO.File.ReadAllLines(textfile)
 lstDisplay.SelectedItem = Nothing
 End Sub 
 

Writting

Dim textfile As String
 Dim swWriteVariable As IO.StreamWriter ‘Make a variable of type StreamWriter
SaveFileDialog1.Filter = “Text Files (*.txt) | *.txt” ‘Show only text files in the save file dialog
 SaveFileDialog1.ShowDialog() ‘Show the save file dialog window
 textfile = SaveFileDialog1.FileName ‘Save the file name in a string variable
 swWriteVariable = IO.File.CreateText(textfile) ‘Create a stream writer to the file
 swWriteVariable.WriteLine(txtEnterData.Text) ‘Write the textbox text into the file
 swWriteVariable.Close() ‘Close the stream reader – very important.
Code
Imports System.Drawing.Printing
Public Class Form1
 Dim pSize As PaperSize
 Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles
MyBase.Load
 Dim InstPrinters As String
 ‘ Find all printers installed
 For Each InstPrinters In _
 PrinterSettings.InstalledPrinters
 cboPrinters.Items.Add(InstPrinters)
 Next InstPrinters
 ‘ Set the combo to the first printer in the list
 cboPrinters.SelectedIndex = 0
 ‘ Put the available paper sizes in a combo box for the user to select
 For i = 0 To PrintDocument1.PrinterSettings.PaperSizes.Count – 1
 pSize = PrintDocument1.PrinterSettings.PaperSizes.Item(i)
 cboPaperSize.Items.Add(pSize)
 Next
 End Sub
 Private Sub btnPrintPreview_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnPrintPreview.Click
 PrintPreviewDialog1.Document = PrintDocument1
 PrintPreviewDialog1.ShowDialog()
 End Sub
 Private Sub PrintDocument1_PrintPage(ByVal sender As System.Object, ByVal e As
System.Drawing.Printing.PrintPageEventArgs) Handles PrintDocument1.PrintPage
 Dim grtext As Graphics = e.Graphics ‘Declars grtext as a graphics object capable of
printing both text and graphics
 Dim font As New Font(“Courier New”, 12, FontStyle.Italic) ‘Define a font that we can
use later
 ‘Now we tell the program what we want to be printed in PrintDocument1
 grtext.DrawString(txtToPrint.Text, Me.Font, Brushes.Black, 100, 150) ‘Uses the forms
Font.
 grtext.DrawString(txtToPrint.Text, font, Brushes.Red, 100, 300) ‘ Uses the font we made
 grtext.DrawString(“This is a test page”, Me.Font, Brushes.Brown, 100, 350)
 End Sub
 Private Sub btnPrint_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
Handles btnPrint.Click
 PrintDocument1.PrinterSettings.PrinterName = cboPrinters.Text ‘Set the printer name
to the selected printer
 PrintDocument1.DefaultPageSettings.PaperSize = pSize ‘set the paper size to
what the user selected
 ‘PrintDocument1.DefaultPageSettings.PaperSize =
PrintDocument1.PrinterSettings.PaperSizes.Item(0)
 PrintDocument1.Print()
 End Sub
End Class