VB.NET編程語法

你這是vb.net的代碼,vb中不允許那么寫:

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Dim

strdx()

As

String

=

{"0",

"0",

"0"}

'定義個數(shù)組,從后面的值能看的出最大下標(biāo)是2,也就是strdx(0),strdx(1)和strdx(2),3個的默認(rèn)值都為0

Dim

calcount1

As

String

=

"0"

'定義個字符串變量

Dim

calcount2

As

String

=

"0"

Dim

strvalue

As

Boolean

=

False

'定義strvalue為bool值,改類型變量只有true和false

2種值

If

strdx(0)

=

"0"

Then

TextBox1.Text

=

strdx(0)

"."

這是字符串連接符號,和"+"的區(qū)別是,他把左右2邊的內(nèi)容直接連接的,而"+"可能會編程運算符,例如

2

3

=

"23"

而

2

+

3

=

5

ElseIf

strvalue

=

False

Then

strdx(0)

=

strdx(0)

"0"

TextBox1.Text

=

strdx(0)

"."

strvalue

=

True

Else

strdx(0)

=

strdx(0)

"0"

TextBox1.Text

=

strdx(0)

Select

Case

calcount1

'

這里開始是分支語句

Case

"+"

TextBox1.Text

=

Str(Val(strdx(1))

+

Val(strdx(0)))

高分求.net里vb語法操作數(shù)據(jù)庫基本語句

Dim Cnn As New Data.OleDb.OleDbConnection

Dim DbAdapter As New Data.OleDb.OleDbDataAdapter

Dim Cmd As New Data.OleDb.OleDbCommand

Dim dsAll As New Data.DataSet

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

Cnn.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=E:\webapp\test\web.mdb"

Cmd.Connection = Cnn

End Sub

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click

'插入

Cmd.CommandText = "insert into main (about) values ('" + TextBox1.Text + "')"

UpdateTable()

End Sub

Protected Sub Button2_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button2.Click

'修改

Dim ids As Integer

ids = 1

Cmd.CommandText = "update main set about='" + TextBox1.Text + "' where id=" + ids.ToString()

UpdateTable()

End Sub

Protected Sub Button3_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button3.Click

'刪除

Dim ids As Integer

ids = 1

Cmd.CommandText = "delete from main where id=" + ids.ToString()

UpdateTable()

End Sub

Public Sub UpdateTable()

Dim Trans As Data.OleDb.OleDbTransaction

Try

Cnn.Open()

Trans = Cnn.BeginTransaction()

Try

Cmd.Transaction = Trans

Cmd.ExecuteNonQuery()

Trans.Commit()

Catch

Trans.Rollback()

Finally

If (Cnn.State = System.Data.ConnectionState.Open) Then

Cnn.Close()

End If

End Try

Catch

'error message

End Try

End Sub

Protected Sub Button4_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button4.Click

'顯示

Cmd.CommandText = "select id, about from main"

DbAdapter.SelectCommand = Cmd

DbAdapter.Fill(dsAll, "table1")

If (dsAll.Tables("table1").Rows.Count 0) Then

TextBox1.Text = dsAll.Tables("table1").Rows(0)("about")

Else

TextBox1.Text = ""

End If

End Sub

VB.net 中，#if 是什么語法？

#If...Then...#Else 指令

根據(jù)條件編譯選定的 Visual Basic 代碼塊,需要有#Const 配對，一般要先用#Const 定義條件編譯器常量

'以下是例子

Module Module1

#Const i = 60

Sub Main()

#If i 30 Then

Console.WriteLine("???") '如果用#Const定義了i，該句語句才會執(zhí)行，假如用的是private i as integer=60定義，該語句不會被執(zhí)行

#End If

End Sub

End Module