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Strings and I/OStrings and I/O

ISAT 252:Analytical Methods ISAT 252:Analytical Methods IVIV

VB.NETVB.NET

AssignmentAssignment

Should have read Chapter 3 pp. 231-241

String Properties and String Properties and MethodsMethods

See pp. 231-241 What does each of these do? str.Length

str.Substring(m, n)

str.IndexOf(str2)

str.ToUpper

str.ToLower

str.Trim

Remember, string indexes start at 0

Conversion of Data typesConversion of Data types

To convert values in a data type to the equivalent value in another data type

Converts non-numeric data (strings|text values) to numeric data Double.Parse() or Integer.Parse() method - Use

to convert input text in a text box/string variable into a number

TotalItemsInteger = Integer.parse("123")

SalesPriceDouble = Double.Parse(txtPrice.Text)

TotalScoreDouble = TotalScoreDouble + _ Double.Parse(txtScore.Text)

ConversionConversion Converts a non-string value in in its equivalent string

of characters

ToString Method Example*

lblOutput.text = (1 + 2 – 3).ToString

lblOutput.text = intItems.ToString

lblOutput.text = (dblTotal*(1 + dblTax)).ToString

*note I am using the shorter naming convention here for a label control. Our book uses OutputLabel.Text = (1 + 2 – 3).ToString, etc.

Problem – compute area of Problem – compute area of circlecircle

Allow user to enter radius

Pseudocode: Declare variables Get input and convert Compute area Display output

Example: compute the area of a Example: compute the area of a circlecircle

Private Sub btnCompute_Click(..) handles _btnCompute.Click

' compute the area of a circleConst dblPI as Double = 3.14

Dim dblRadius As DoubleDim dblCircleArea As Double

‘Convert the input radius into a number dblRadius = CDbl(txtRadius.Text)

'compute the area of the circle dblCircleArea = dblPI * dblRadius ^ 2 'output the area of the circle txtOut.Text = "The area of the circle is " + _ dblCircleArea.ToString & " inches“End Sub

Data declaration

Input and convert the appropriate values

Calculation

Output

Displaying Text OutputDisplaying Text Output

Labels Multiple lines, but it will not allow the user

to scroll when all the lines are not visible Use CStr or To.String to convert

numbers to string List Boxes

Use lstName.Items.Add( ) for each line Use CStr or To.String to convert

numbers to string

Message Boxes See p. 140

Displaying Text OutputDisplaying Text Output

TextboxTextbox When ReadOnly Property set to TRUE, a

textbox is strictly an output control You can display multiple lines in a textbox

by setting the property Multiline to TRUE You can allow the user to scroll

horizontally and vertically by setting the appropriate scrollbars in the property Scrollbars

Use CStr or To.String to convert numbers to string

Formatted OutputFormatted Output

Can adjust spacing by inserting blanks blanks should be within the quote marks works best with a fixed size font such as

Courier

Numeric Output can use pre-defined formats such as

“FormatCurrency” and “FormatPercent” can create custom columnar formats

using zones

Formatting Data for DisplayFormatting Data for Display

To display numeric data in a label or text box, first convert value to string.

Use ToString method

Format the data using formatting codes.Specifies use of dollar sign, percent sign,

and commasSpecifies number of digits that appear to

right of decimal point

DisplayTextBox.Text = NumberInteger.ToString()

Using Format Specifier Using Format Specifier CodesCodes

"C" codeCurrency — String formatted with dollar

sign, commas separating each group of 3 digits and 2 digits to the right of decimal point

"N" codeNumber — String formatted with commas

separating each group of 3 digits and 2 digits to the right of decimal point

Can specify number of decimal positionsExample: "C0" zero digits

Format Specifier CodesFormat Specifier Codes

Format Specifier Codes Name

C or c Currency

F or f Fixed-point

N or n Number

D or d Digits

P or p Percent

Format Specifier Code Format Specifier Code ExamplesExamples

Variable Value Code Output

totalDecimal 1125.6744 "C" $1,125.67

totalDecimal 1125.6744 "N0" 1,126

pinInteger 123 "D6" 000123

rateDecimal 0.075 "P" 7.50%

rateDecimal 0.075 "P3" 7.500%

rateDecimal 0.075 "P0" 8%

valueInteger -10 "C" ($10.00)

Getting InputGetting Input

From a TextboxFrom a Textbox Always a string Use Double.Parse or Integer.Parse if you

are putting values into number variableOR

You can use CDbl or CInt if you are putting values into number variables

From an Input Dialog Box See Textbook

Getting Input Getting Input From Files see p. 541-546

1. Declare the file

Dim readerVar As IO.StreamReader

2. Open the file

readerVar = IO.File.OpenText (filespec)

3. Read from file

strVar = readerVar.ReadLine

numVar = Double.Parse (readerVar.ReadLine)

( OR numVar = CDbl (readerVar.ReadLine) )

4. Close the file

readerVar.Close()

Example of Reading from Example of Reading from FilesFiles

Private Sub ReadFileButton_Click() Handles ReadFileButton.Click

Dim strName1 As String

Dim strName2As String

Dim fileNames As IO.StreamReader

fileNames = IO.File.OpenText("Names.txt")

‘Names.txt is in the Debug folder of the bin for the project

strName1 = fileNames.ReadLine

strName2 = fileNames.ReadLine

fileNames.Close()

txtOutput.Text = strName1+ " and " + strName2

End Sub

AssignmentsAssignments

Do Lab 6 and Lab 7 Answer the Question Sheet

Next Lecture Read Chapter 4 (pages 205 – 252) Do Tutorials

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