vb.net语法笔记,VBNET编程宝典

VB.NET的 把重点的语句注释下就行了

'''两段程序就是利用.net的连接对象的功能来完成登录的实例

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Private Sub btnStart_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnStart.Click 'start按钮触发的函数

Dim schclass As String = Trim(txtClass.Text) ‘将txtClass里文本赋值给变量schclass

Dim selestr As String

’提示用户txtClass文本框不能为空

If schclass "" Then

selestr = "班级='" schclass "'"

Else

MsgBox("请输入班级名称", 64, "提示") ‘ 显示保存成功提示信息

End If

‘创建一个DataView对象，即将数据集DataSet11里的学生成绩表的DefaultView实例化

Dim dvresult As DataView = DataSet11.学生成绩.DefaultView

’按学号字段排序

dvresult.Sort = "学号"

‘按刚才txtClass里输入的班级查询

dvresult.RowFilter = selestr

dvresult.RowStateFilter = DataViewRowState.CurrentRows

’然后将筛选的结果输入到datagrid上

DataGrid1.DataSource = dvresult

End Sub

Private Sub btnOK_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnOK.Click ‘ok按钮触发的函数

’如果txtUserName或txtPass文本框为空，提示并中断函数

If txtUserName.Text = "" Or txtPass.Text = "" Then

Response.Write("script language=vbscriptalert""用户名或密码不能为空！""/script")

Exit Sub

End If

‘定义链接、执行、阅读 对象

Dim mycon As New OleDbConnection

Dim mycmd As New OleDbCommand

Dim reader As OleDbDataReader

’给连接对象赋值连接字符串，access类型的。

mycon.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" _

Server.MapPath("Msg.mdb")

‘打开连接对象

mycon.Open()

’将连接对象复制到执行对象上

mycmd.Connection = mycon

‘然后就给执行对象赋值执行类型和执行语句

mycmd.CommandType = CommandType.Text

mycmd.CommandText = "Select * from myuser Where 用户名='" txtUserName.Text "'" " and 密码='" txtPass.Text "'"

’然后将执行对象的监听实例化

reader = mycmd.ExecuteReader()

‘如果执行不成功，即没有得到结果集就提示否则将结果集的用户名赋值给一个session以供其他页面使用

If reader.Read = False Then

Response.Write("script language=vbscriptalert""用户名或密码错，你不能登录！""/script")

Else

Session("username") = reader("用户名")

Response.Redirect("lwmsg.aspx")

End If

’关闭监听

reader.Close()

‘关闭连接

mycon.Close()

End Sub

vb.net查询语法

顺序应该是先Connection的Open

con.ConnectionString = constr

con.Open()

dc = New OleDbDataAdapter(sql, constr)

另外你的SQL语句好像有点问题，表名不加单引号

VB.NET编程语法

你这是vb.net的代码,vb中不允许那么写:

Dim

strdx()

As

String

=

{"0",

"0",

"0"}

'定义个数组,从后面的值能看的出最大下标是2,也就是strdx(0),strdx(1)和strdx(2),3个的默认值都为0

Dim

calcount1

As

String

=

"0"

'定义个字符串变量

Dim

calcount2

As

String

=

"0"

Dim

strvalue

As

Boolean

=

False

'定义strvalue为bool值,改类型变量只有true和false

2种值

If

strdx(0)

=

"0"

Then

TextBox1.Text

=

strdx(0)

"."

这是字符串连接符号,和"+"的区别是,他把左右2边的内容直接连接的,而"+"可能会编程运算符,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

'

这里开始是分支语句

Case

"+"

TextBox1.Text

=

Str(Val(strdx(1))

+

Val(strdx(0)))

高分求.net里vb语法操作数据库基本语句

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

'删除

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

'显示

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 goto语法

你这个问题是这样的呀：

因为你输入了10+10以后你为了结束是不是又打了个回车？那就是\n了，

但是这个\n现在被存在stdin的缓冲区里没有被取走，所以当你要输入Y或者N的时候，again将stdin的\n取走了，而没有给你输入的机会。

所以你应该是

printf("Please enter Y or N\n");

scanf("%c", again); //取走\n

scanf("%c",again); //记录Y或者N

这样就可以了。