1 microsoft® visual basic®.net language # 1. 2 variable declaring variable dim {variablename} as...
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Microsoft®Visual Basic® .NET
Language# 1
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Variable
Declaring Variable
Dim {VariableName} As {Type}
Dim {VariableName} As {Type} = {value}
Example:
Dim var1 As String
Dim Var2, Var3, Var4 As String
Example:
Dim var1 As String = "Hello World"
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Data Types
Five Categories
Numeric
Boolean
String
Date
Object
Integrated in the common language runtime
2 Varieties of Data Types
Value Types
Reference Types
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Numeric Data Types
Data Type Memory Representation
Stores
Byte 1 byte Positive integer value0 to 255
Short (Int16) 2 bytes Integer value -32768 to 32767
Integer (Int32)
4 bytes Integer value -2,147,483,648 to 2,147,483,647
Long (Int64) 8 bytes Vary large integer value.-263 to (263-1)
Single 4 bytes Single-precisionfloating-point number.
Double 8 bytes Double-precisionfloating-point number.
Decimal 16 bytes Vary-Vary large integer and floating-point number
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Not Number Data Types.
Boolean True / False
String Store only text data.
Character Store only one character.
DateTime Store Date and Time Data.
Example :Var1 = #01/01/2003#Var2 ="Sep 1,1977"Var3 = #01/01/2003 6:25:11 PM#Var4 = Now()
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Value Types (Numeric, Boolean, String, Date)
Store Data in Stack Memory
Function A
Dim Var1 As String = "AAA"
Call B
End Function
Function B
Dim Var2 As String = "BBB"
Call C
End Function
Function C
Dim Var3 As String = "CCC"
End Function
Stack Memory
(LastInFirstOut)
Var1="AAA"
Var2="BBB"
Var3="CCC"
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Reference Types (Object)
Store Variable in Stack Memory
Store Data in Heap Memory
Function A
Dim Var1 As ObjA
Var1 = New ObjA
Var1.Data = "ZZZ"
End Function
Stack Memory
Var1
ObjA
Heap Memory
Data = "ZZZ"
GC
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Data Type Functions
GetType( {Variable} ) IsNumeric( {Variable} ) IsDate( {Variable} ) IsReference( {Variable} )
Conversion Data Types
CBool CByte CChar
CDate CDbl CDec
CInt CLng CShort
CSng CStr CType
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Parse Method
To convert a numeric string to a numeric or others, use the Parse method
To Ignore Commas, Use the NumberStyles.AllowThousands Flag
Dim MyString As String = “12345”
Dim MyInt As Integer = Integer.Parse(MyString)
MyInt += 1
Console.WriteLine(MyInt)
‘ The output to the console is “12346”
Dim MyString As String = “123,456”
Dim MyInt As Integer = Integer.Parse(MyString, _
Globalization.NumberStyles.AllowThousands)
Console.WriteLine(MyInt)
‘ The output to the console is “123456”
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Constant
Once a constant has been declared
Cannot change value.
Process faster than variable.
Const { ConstantName } As Type = Value
Example :
Const pi As Double = 3.14159265358979
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Array
Set of data which have the same type.
Zero based.
Declaring Array
Dim MyString (5) As String
MyString(3) = "Happy"
Dim str as String
str = MyString(3) ‘str = "Happy"
MyString(5)
MyString(4)
MyString(3) Happy
MyString(2)
MyString(1)
MyString(0)
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String
Trim method
remove spaces
Pad method
Expand a specific number of characters
Dim MyString As String = “ Big ”
Dim TrimString As String = MyString.Trim()
Console.WriteLine(TrimString)
‘The output to the console is “Big”
Dim MyString As String = “Hello World!”
Console.WriteLine(MyString.PadLeft(20, “-”))
‘The output to the console is “--------Hello World!”
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Changing Case
Methods that compare strings and characters are case-sensitive
Convert the case of strings that are entered by users before comparing them
To change the case of a string use:
String.ToUpper
String.ToLower
Dim MyString As String = “hello world!”
Console.WriteLine(MyString.ToUpper())
‘The output to the console is “HELLO WORLD!”
Dim MyString As String = “HELLO WORLD!”
Console.WriteLine(MyString.ToLower())
‘The output to the console is “hello world!”
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Split and Join
Split method breaks up a string into an array of substrings
String is broken at positions indicated by the specified separator characters parameter
If the separator parameter is Nothing, the white-space characters are assumed to be the separator
Join method concatenates a specified separator between string array
A specified separator string is placed between each element of a string array
Dim Line As String = “hello world”
Dim Words() As String = Line.Split(“ ”)
‘Words(0) = “hello” and Words(1) = “World”
Dim MyString() As String = {“apple”, “orange”, “grape”, “pear”}
Dim JoinString as String = String.Join(“/”, MyString, 0, 3)
‘JoinString = “apple/orange/grape”
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Length and IndexOf
Length Method
Gets the number of characters in this instance
IndexOf Method
Reports the index of the first occurrence of a string or one or more characters, within this instance.
Dim MyString As String = “Hello World!”
Console.WriteLine(MyString.Length())
‘The output to the console is “12”
Dim MyString As String = “Hello World!”
Console.WriteLine(MyString.IndexOf(“or”)
‘The output to the console is “7”
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Operators
Arithmetic Operators
+ - * / += -= *= /=
A = 2 + 3 B += 5 C = B / 2
String Operators
+ &
Message = "Hello " + Name
Boolean Operators
= < > <= >= <>
And Or Not AndAlso OrElse
If A=5 AndAlso B>6 Then