VB variable types and control statements (basic)

Section 1 ： Data types and common control statements

1、 Operator ：

（1） Assignment operator =

（2） Mathematical operators ： &、+ ( Character connector )、+( Add )、-（ reduce ）、*（ ride ）、/（ except ）、Mod（ Remainder ）、\（ to be divisible by ）、-（ Minus sign ）、^（ Index ）

（3） Logical operators ：Not（ Not ）、And（ And ）、Or（ or ）、Xor（ Exclusive or ）、Eqv（ equal ）、Imp（ Implication ）

（4） Relational operator ： = （ equal ）、<>（ Unequal ）、>（ Greater than ）、<（ Less than ）、>=（ Not less than ）、<=（ No more than ）、Like、Is

（5） An operator Not（ Logic is not ）、And（ Logic and ）、Or（ Logic or ）、Xor（ Logical XOR ）、Eqv（ Logic, etc. ）、Imp（ Implication ）

2、 data type ：

         VBA share 12 Type of data , See the following table for details , In addition, users can also use... According to the following types Type Custom data types .

data type	Type identifier	byte
String type String	$	Character length (0-65400)
Byte type Byte	nothing	1
Boolean type Boolean	nothing	2
Integer type Integer	%	2
Long integer type Long	&	4
Single precision type Single	!	4
Double precision type Double	#	8
Date type Date	nothing	8 A.D. 100/1/1-9999/12/31
Currency type Currency	@	8
Decimal point type Decimal	nothing	14
Variant Variant	nothing	Any of the above types , variable
Object type Object	nothing	4

3、 Variables and constants

（1）VBA Allow undefined variables , Variant variable by default Variant.

（2） In the general description of the module , Join in Option Explicit Statement can force the user to define variables .

（3） Variable definition statement and variable scope

Dim          Variable as type	' Defined as a local variable	Such as Dim        xyz  as  integer
Private      Variable as type	' Define as private variable	Such as Private    xyz  as  byte
Public       Variable as type	' Defined as a public variable	Such as Public     xyz  as  single
Global       Variable as type	' Defined as a global variable	Such as Globlal    xyz  as  date
Static       Variable as type	' It's defined as a static variable	Such as Static     xyz  as  double

     The principle of the general variable scope is , That part of the definition works in that part , The definition in the module is used in the module .

（4） Constant is a special case of variable , use Const Definition , And assigned when defined , Value cannot be changed in program , Scope is also like variable scope .

      As defined below ：Const Pi=3.1415926 as single

4、 Array

      In memory, it appears as a continuous memory block , Must use Global or Dim To define . The rules of definition are as follows ：Dim Array name ([lower to ]upper [, [lower to ]upper, ….]) as type ;Lower The default value is 0. Two dimensional arrays are arranged in rows and columns , Such as XYZ( That's ok , Column ). In addition to the above fixed array ,VBA There is also a powerful dynamic array , There is no size dimension declaration when defining ; Reuse in the program Redim Statement to resize the array , The contents of the original array can be added preserve Keywords to keep . Here's an example ：Dim array1() as double : Redim array1(5) : array1(3)=250 : Redim preserve array1(5,10)

5、 notes

        Comment statement is used to explain the function and function of some statements in the program ;VBA There are two ways to identify them as comment statements in . Single quotation marks ’ ; Such as ：’ Define global variables ; Can be at the end of other statements , It can also be a single line Rem ; Such as ：Rem Define global variables ; Only one line .

6、 Writing norms

（1）VBA Don't distinguish the case of the identifier , It's all lowercase ;

（2） You can write multiple sentences in one line , Colon between statements : Separate ;

（3） A statement can be written in multiple lines , Underline with spaces _ To identify line continuation ;

（4） It's best to keep the identifier simple , No ambiguity .

 

In the second quarter ： Common control statements and examples

1、 Judgment statement  If … Then … Else  Endif sentence

If a>60 Then
    k=1
Elself a>70 Then
    k=2
Elself a>80 Then
    k=3
Elself a>90 Then
    k=4
Endif

2、Select Case sentence

      Select Case Time
            Case 1 To 11
                  msg = " In the morning "
            Case 12
                  msg = " At noon, "
            Case 13 To 16
                  msg = " Afternoon "
            Case 17 To 20
                  msg = " evening "
            Case 23, 24
                  msg = " The middle of the night "
            Case Else
                  msg = " Unknown "
      End Select

      MsgBox " Now it is ：" & msg

3、 Loop statement

（1）For … Next loop

For cnt = 1 To 10 Step 1             '  establish  10  Secondary cycle 

    For Chars = 0 To 9                    '  establish  10  Secondary cycle 

        MyString = MyString & Chars            '  Add a number to the string 

    Next Chars                            ' Increment counter

    MyString = MyString & " "           '  Add a space 

Next cnt
[Exit For]

（2）For Each…Next sentence

      The main function is to set an array or collection object , Let all elements execute the statement again

Sub  Greater than 90 Cells of are painted red ()

    Dim rng  As Range

    For Each rng In Sheet5.Range("b3:b12")
      Select Case rng
      Case Is >= 90
      rng.Interior.ColorIndex = 3
      End Select
    Next

End Sub

Other common cycles

1) Do While loop 
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Do [While  Conditions ]
  [ Instructions ]
  [Exit Do]
  [ Instructions ]
Loop

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Do
  [ Instructions ]
  [Exit Do]
  [ Instructions ]
Loop [While  Conditions ]
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2) Do Until loop 
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Do [Until  Conditions ]
  [ Instructions ]
  [Exit Do]
  [ Instructions ]
Loop
---------------------------------------------------------
Do
  [ Instructions ]
  [Exit Do]
  [ Instructions ]
Loop [Until  Conditions ]

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3) While … Wend loop 

While < Conditions >
  [ Instructions ]
Wend