VB learning process (ii) The grammatical basis of VB and the commonly used intrinsic function __ function

2013/11/01 Reprint Please specify Source: http://blog.csdn.net/lxk7280

Syntax Basics:

(1) Sequential structure

Private Sub Form_Load ()
   Dim Num1 as Integer, Num2 as inteher
   Num1 = 1 
   Num2 = 2
   MsgBox Num2
End Sub

The program executes from top to bottom, there is no jump or loop, and runs to end Sub.

This is called the sequential structure.

(2) Select structure

There are various, such as: If statement, multi-branch if statement, Select case statement.

Private Sub Form_Load ()  
   Dim num as Integer
   num = 1
   If num = 1 then
      num = 2
   Else
      num = 3
   End If
   MsgBox Num
End Sub

The choice of structure is that the program chooses whether to execute the current statement based on the criteria you give.

(3) Cycle structure

The loop structure contains various, such as: For Loop, while loop, for each Next loop, etc.

Private Sub Form_Load ()
   Dim I as Integer do while
   i <=
      s = s + i
      i  = i + 1
   Loop
   MsgBox "1 to 100 and yes" & S
End Sub

Several intrinsic functions are commonly used:

1.Trim function: Used to delete spaces on both sides of a string.

Private Sub Form_Load ()
   Dim Str as String
   str = "    Can you?   "
   Magbox str
   str = Trim (str)
   MsgBox str
End Sub

2.Mid function: Mid (string, starting position, length) For example: Mid (str,4,1); Starting from the fourth bit of the string str, intercept a character

3.Len function: Calculating the length of a string

4.Left function: The first bit from the left of a string to intercept, a number of characters.

5.Right function: The first bit from the right of a string to intercept, a number of characters.

6.Instr function: Used to determine whether the string 2 appears in string 1, and where it appears. For example: Instr (str1, "God")

7.ASC function: Returns the ASCII code of a character

8.CHR function: The exact opposite of the ASC function

9.Lcase function: The character is converted to lowercase.

10.Ucase function: The exact opposite of the LCase function.

☆11. MsgBox Function:

vbOKOnly: Show only OK button

Vbokcance: Show only OK and Cancel buttons

Vbabortretrylgnorel: Show Abort Retry Ignore button

vbYesNoCancel: Show Yes No Cacel button

vbYesNo: Show Yes No button

Vbretrycancel: Show retry Cancel button

Vbcritical: Display critical message icon

vbquestion: Display warning query icon

Vbexclamation: Display warning message icon

vbinformation: Display information message icon

VbDefaultButton1: The first button is a default value

VbDefaultButton2: Second push-button default value

VbDefaultButton3: Third Push-button default value

VbDefaultButton4: The fourth button is a default value

For example:

MsgBox "Do you love Me?", vbYesNo, "Ask:"

MsgBox "You is right!", vbinformation, "Yes"

Default value: The computer software system requires the user to enter certain values while the user is not given, the system automatically assigns a predetermined value.

The MsgBox function has a return value, and the following describes its return value (int type):

vbOK: Pressed OK

Vbcancel: Press Cancel

Vbabort: The abort was pressed

Vbretry: pressed the retry

Vbignore: pressed the Ignore

Vbyes: Pressed Yes

Vbno: Pressed No

12.dir function

Basic form: Dir (path, attribute)

Possible values for the property:

Vbnormal: Default file with no attributes

vbReadOnly: Read-only file with no attributes

Vbhidden: Hidden files with no attributes

Vbsystem: System files with no attributes

VbVolume: Volume label file

Vbdirectory: No properties files and paths and folders

For example:

Dim file as String
file = Dir ("D:\test\")

After running these two lines, file will be the name of the first file in the test file under the D drive.

13.SetAttr function

Used to set properties for files and folders.

Optional value of the property:

Vbnormal: General

vbReadOnly: Read-only

Vbhidden: Hide

Vbsystem: System files

Vbarchive: The file has changed since the last backup

For example:

SetAttr "D:\test", Vbhidden + Vbsystem

After executing this sentence, the test folder is hidden. There are a lot of ways to get him back, and here are two of them.

One is to open any system disk when the settings open, set to show hidden folders, the general computer default is not to show hidden files.

Another is to use the SetAttr function in VB6.0 to manipulate the file, the statement is:

SetAttr "D:\test", vbnormal

This chapter is to write a little bit, the following a few simple procedures:

Private Sub Form_Load ()
    Dim answer As Integer
    Dim A As String, B As String
    answer = MsgBox ("Do You Love Me?",  vbquestion + vbYesNo, "ask:")
    If answer = vbyes Then
        a = Dir ("D:\test\") while
        a <> vbnullstring
            b = A & Chr & Chr10 & B
            a = Dir
        wend
        MsgBox b
        SetAttr "D:\test", vbnormal ' Vbhidden + vbsyst EM
    Else
        
    End If
End Sub

Here is the effect diagram of this program: