1. Strings(Part 1) String Literal and String Variable
Declaration and Initialization
Using String in Input and Output

2. String
String literal
a sequence of characters treated as a single item, surrounded by “”
String variable
a name used to refer to a string
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Strings

3. String declaration and Initialization
Dim varName As String
Initialization
Dim today As String = "Monday“
Dim today As String = "“
A string should be assigned a value before being used .By default the initial value is Nothing
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4. Using Strings strVar = txtBox.Text txtBox.Text = strVar
Using Text Boxes for Input and Output
The contents of a text box is a string
input
strVar = txtBox.Text
Output (ReadOnly = true)
txtBox.Text = strVar
String literal can be displayed in list box
lstBox.Items.Add(“Monday”)
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5. Data Conversion(Type – Casting)
Conversion from one dataType to another, Such as
numVar = CDbl(txtBox.Text)
numVar = CSng(txtBox.Text)
numVar = CInt(txtBox.Text)
txtBox.Text = CStr(numVar)
All conversions to String are considered to be widening, regardless of whether strict semantics are used
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6. Code
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7. Code ' The celsius temperature is converted into Fahrenheit
Private Sub btnConvert_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnConvert.Click
Dim tempC As Single
Dim tempF As Single
Dim tempFStr As String
' Get the temp from user
tempC = CSng(txtTemp.Text)
' Convert tempC to TempF
tempF = (tempC * 9 / 5) + 32
' Display tempF in the list box
tempFStr = CStr(tempF)
lstTemp.Items.Add(tempFStr)
End Sub
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8. Concatenation
Combining two strings into a new string.Concatenation is represented by “&”
Dim str1 As String = “My grade "
Dim Str2 As String = “is A"
txtOutput.Text = str1 & str2
My grade is A
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9. Concatenation Combining strings with numbers into a string
Dim str As String = “My grade is “
Dim grade As Double = 89
txtOutput.Text = str & grade
displays
My grade is 89
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10. Code Editing code The temperature is 80F
lstTemp.Items.Add( “ The temperature is “ & tempFStr & “F”)
Displays
The temperature is 80F
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11. ANSI Character Set
A numeric representation for every key on the keyboard. The numbers are ranging from 32 to 255
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12. ANSI Character Set If n is between 32 and 255, str
Chr(n):returns the string consisting of the
character with ANSI value n
Chr(65) A
Asc(str):returns the ANSI value of the first
character of str
Asc(“Apple”)
32 & Chr(176) & “Fahrenheit ° Fahrenheit
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13. String Properties and Methods Option Statements Internal Documentation
Strings(Part 2)
String Properties and Methods
Option Statements
Internal Documentation

14. String Properties and Methods
A string is an object, like controls, has both properties and methods.
Length
ToUpper
Trim
ToLower
IndexOf
Substring
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15. String Properties (Length)
str.Length:
the number of characters in str
Dim str As String = “Tacoma“
str.Length is 6
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16. ToUpper and ToLower str.ToUpper str.ToUpper() is TACOMA. str.ToLower
with all letters of str capitalized
str.ToUpper() is TACOMA.
str.ToLower
with all letters of str in lowercase format
str.ToLower() is tacoma
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17. Trim, TrimStart, TrimEnd
str.Trim
with all leading and trailing spaces deleted
Dim str As String = “ Tacoma “
str.Trim() Tacoma
str.TrimStart() -- “Tacoma “
str.TrimEnd() “ Tacoma”
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18. Sunstring str.Substring(m,n) str.Substring(m)
substring consisting of n characters
beginning with the character in position m in
str
str.Substring(m)
substring beginning with the character in
position m in str until the end of str
Dim str As String = “Tacoma”
str.Substring(0,4) is “Taco”
str.Substring(2) is “coma”
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19. IndexOf str.IndexOf(substr) -1 if substr is a substring of str
other wise, beginning position of the first occurrence of substr in str
Dim str As String = “Tacoma”
str.IndexOf("ati") is -1.
str.IndexOf(“co") is 2.
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20. IndexOf str.IndexOf(substr,n) the position of the first occurrence of
substr in str in position n or greater
"fantastic".IndexOf(“a”, 3) is 4.
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21. The Empty String zero-length string ""
lstBox.Items.Add("") skips a line
txtBox.Text = "“ clear the text box
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22. Code
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23. Code
' Get the area code and phone number and display them
Private Sub btnAnalyze_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAnalyze.Click
Dim phoneNum As String
Dim areaCode As String
Dim num As String
Dim index As Integer
' Get the phone number entered by user
phoneNum = txtPhoneNo.Text
' Find the area code and number
phoneNum = phoneNum.Trim()
index = phoneNum.IndexOf("-")
areaCode = phoneNum.Substring(0, index)
num = phoneNum.Substring(index + 1)
' Display the area code and number
lstPhoneNo.Items.Clear()
lstPhoneNo.Items.Add(" Your area code is " & areaCode)
lstPhoneNo.Items.Add(" Your number is " & num)
End Sub
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24. Option Statements Statement is placed at the very top of code window
Option Explicit { On | Off}
used at file level to force explicit declaration of all variable in that file, default value is On
Option Strict { On | Off }
used at file level to enable or disable strict type checking, default value is Off
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25. Option Explicit
When Option Explicit is On, all variables must be declared explicitly using Dim, Private, Public or ReDim
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26. Option Strict
Restricts implicit data type conversions to only widening conversions
Provides compile-time notification of data lost conversions
Generates an error for any undeclared variable
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27. Code
ConvertTempCToF
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28. Internal Documentation
Begin the line with an apostrophe
Benefits:
Easy to understand the program
Easy to read long programs because the purposes of individual pieces can be determined at a glance.
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29. Line-Continuation Character
A long line of code can be continued on another line by using underscore (_) preceded by a space
msg = “Today is the day “ & _
“ that everybody will have fun"
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