我是個VB初學者誰能給我解釋一下VB中的 :Exp,log,是干什么的還有怎么用??

log:

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說明VB不支持ln函數(shù)，換句話說，VB的log函數(shù)就是數(shù)學中的ln函數(shù)，而常用對數(shù)lg只能使用換底公式lg(x)=log(x)/log(10)條件很簡單x0。

Log

函數(shù)

返回一個

Double，指定參數(shù)的自然對數(shù)值。

語法

Log(number)

必要的

number

參數(shù)是

Double

或任何有效的大于

的數(shù)值表達式。

說明

自然對數(shù)是以

e

為底的對數(shù)。常數(shù)

e

的值大約是

2.718282。

如下所示，將

x

的自然對數(shù)值除以

n

的自然對數(shù)值，就可以對任意底

n

來計算數(shù)值

x

的對數(shù)值：

Logn(x)

=

Log(x)

/

Log(n)

下面的示例說明如何編寫一個函數(shù)來求以

10

為底的對數(shù)值：

Static

Function

Log10(X)

Log10

=

Log(X)

/

Log(10#)End

Function

exp:

Exp

函數(shù)

返回

Double，指定

e（自然對數(shù)的底）的某次方。

語法

Exp(number)

必要的

number

參數(shù)

number

是

Double

或任何有效的數(shù)值表達式。

說明

如果

number

的值超過

709.782712893，則會導致錯誤發(fā)生。常數(shù)

e

的值大約是

2.718282。

注意

Exp

函數(shù)的作用和

Log

的作用互補，所以有時也稱做反對數(shù)。

利用VB.NET實現(xiàn)導出DataTable數(shù)據(jù)到excel中，各位大俠幫幫忙，最好有源碼，謝謝，江湖救急

剛好寫了個Helper類，你試驗一下DataTable2Exce(這個方法代碼如下：

Imports System.IO

Imports System.Data

Imports System.Data.OleDb

Public MustInherit Class ExcelHelper

Private Shared Function buildConnStr(excelFilePath As String) As String

Dim excelFileInfo As New System.IO.FileInfo(excelFilePath)

Dim constr As String

If excelFileInfo.Extension = ".xlsx" Then

constr = String.Format("Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties='Excel 12.0 Xml;HDR=YES;IMEX=1'", excelFilePath)

Else

constr = String.Format("Provider=Microsoft.Jet.OLEDB.4.0;Data Source={0};Extended Properties='Excel 8.0;HDR=Yes;IMEX=1'", excelFilePath)

End If

Return constr

End Function

'將datatable導入到excel

Public Shared Function DataTable2Excel(dt As DataTable, excelFilePath As String) As Boolean

If File.Exists(excelFilePath) Then

Throw New Exception("該文件已經(jīng)存在！")

End If

If dt.TableName.Trim.Length = 0 Or dt.TableName.ToLower = "table" Then

dt.TableName = "Sheet1"

End If

Dim colCount As Integer = dt.Columns.Count

Dim pa(colCount - 1) As OleDb.OleDbParameter

Dim tableStructStr As String = "Create Table " dt.TableName "("

Dim connString As String = buildConnStr(excelFilePath)

Dim objconn As New OleDbConnection(connString)

Dim objcmd As New OleDbCommand

objcmd.Connection = objconn

Dim dataTypeList As New ArrayList

dataTypeList.Add("System.Decimal")

dataTypeList.Add("System.Double")

dataTypeList.Add("System.Int16")

dataTypeList.Add("System.Int32")

dataTypeList.Add("System.Int64")

dataTypeList.Add("System.Single")

Dim i As Integer = 0

For Each col As DataColumn In dt.Columns

If dataTypeList.IndexOf(col.GetType.ToString) 0 Then

pa(i) = New OleDbParameter("@" col.ColumnName, OleDbType.Double)

objcmd.Parameters.Add(pa(i))

If i + 1 = colCount Then

tableStructStr += col.ColumnName + " double)"

Else

tableStructStr += col.ColumnName + " double,"

End If

Else

pa(i) = New OleDbParameter("@" col.ColumnName, OleDbType.VarChar)

objcmd.Parameters.Add(pa(i))

If i + 1 = colCount Then

tableStructStr += col.ColumnName + " VarChar)"

Else

tableStructStr += col.ColumnName + " VarChar,"

End If

End If

i += 1

Next

Try

objcmd.CommandText = tableStructStr

If objconn.State = ConnectionState.Closed Then objconn.Open()

objcmd.ExecuteNonQuery()

Catch ex As Exception

Throw ex

End Try

Dim InsertSql_1 As String = "Insert into " + dt.TableName + " ("

Dim InsertSql_2 As String = " Values ("

Dim InsertSql As String = ""

For colID As Integer = 0 To colCount - 1 Step 1

If colID + 1 = colCount Then

InsertSql_1 += dt.Columns(colID).ColumnName ")"

InsertSql_2 += "@" + dt.Columns(colID).ColumnName + ")"

Else

InsertSql_1 += dt.Columns(colID).ColumnName + ","

InsertSql_2 += "@" + dt.Columns(colID).ColumnName + ","

End If

Next

InsertSql = InsertSql_1 + InsertSql_2

For rowID As Integer = 0 To dt.Rows.Count - 1 Step 1

For colID = 0 To dt.Columns.Count - 1

If pa(colID).DbType = DbType.Double And dt.Rows(rowID)(colID).ToString.Trim = "" Then

pa(colID).Value = 0

Else

pa(colID).Value = dt.Rows(rowID)(colID).ToString.Trim

End If

Next

Try

objcmd.CommandText = InsertSql

objcmd.ExecuteNonQuery()

Catch ex As Exception

Throw ex

End Try

Next

Try

If objconn.State = ConnectionState.Open Then objconn.Close()

Catch exp As Exception

Throw exp

End Try

Return True

End Function

' 獲取Excel文件數(shù)據(jù)表列表Sheets

Public Shared Function GetExcelTables(ExcelFileName As String) As ArrayList

'Dim sheets As New List(Of String)

'conn.Open()

'Dim dt As DataTable = conn.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, Nothing)

'For Each r In dt.Rows

' sheets.Add(r("TABLE_NAME"))

'Next

'conn.Close()

'Return sheets

Dim dt As DataTable

If Not File.Exists(ExcelFileName) Then

Throw New Exception("指定的Excel文件不存在")

Return Nothing

End If

Dim tableList As New ArrayList

Using conn As OleDbConnection = New OleDbConnection(buildConnStr(ExcelFileName))

Try

conn.Open()

dt = conn.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, New Object() {Nothing, Nothing, Nothing, "TABLE"})

Catch ex As Exception

Throw ex

End Try

For i As Integer = 0 To dt.Rows.Count - 1

Dim tableName As String = dt.Rows(i)(2).ToString.Trim.TrimEnd("$")

If tableList.IndexOf(tableName) 0 Then tableList.Add(tableName)

Next

End Using

Return tableList

End Function

'將Excel文件導出至DataTable(第一行作為表頭)

Public Shared Function InputFromExcel(ExcelFileName As String, TableName As String) As DataTable

If Not File.Exists(ExcelFileName) Then

Throw New Exception("指定的Excel文件不存在")

End If

Dim tableList As ArrayList = GetExcelTables(ExcelFileName)

If tableList.IndexOf(TableName) 0 Then

TableName = tableList(0).ToString.Trim

End If

Dim dt As New DataTable

Dim conn As New OleDbConnection(buildConnStr(ExcelFileName))

Dim cmd As New OleDbCommand("select * from [" TableName "$]", conn) '調(diào)試是否需要$

Dim adapter As New OleDbDataAdapter(cmd)

Try

If conn.State = ConnectionState.Closed Then conn.Open()

adapter.Fill(dt)

Catch ex As Exception

Throw ex

Finally

If conn.State = ConnectionState.Open Then conn.Close()

End Try

Return dt

End Function

'查詢excel文件中的一個數(shù)據(jù)

Public Shared Function ReadOneDataFromExcel(ExcelFileName As String, TableName As String, sql As String) As Object

If Not File.Exists(ExcelFileName) Then

Throw New Exception("指定的Excel文件不存在")

End If

Dim tableList As ArrayList = GetExcelTables(ExcelFileName)

If tableList.IndexOf(TableName) 0 Then

TableName = tableList(0).ToString.Trim

End If

Dim dt As New DataTable

Dim conn As New OleDbConnection(buildConnStr(ExcelFileName))

Dim cmd As New OleDbCommand(sql, conn) '調(diào)試是否需要$

Dim ret As Object

Try

If conn.State = ConnectionState.Closed Then conn.Open()

ret = cmd.ExecuteScalar()

Catch ex As Exception

Throw ex

Finally

If conn.State = ConnectionState.Open Then conn.Close()

End Try

Return ret

End Function

'獲取Excel文件指定數(shù)據(jù)表的數(shù)據(jù)列表columnNames

Public Shared Function GetExcelTableColumns(ExcelFileName As String, TableName As String) As ArrayList

Dim dt As DataTable

If Not File.Exists(ExcelFileName) Then

Throw New Exception("指定的Excel文件不存在")

Return Nothing

End If

Dim ColList As New ArrayList

Using conn As OleDbConnection = New OleDbConnection(buildConnStr(ExcelFileName))

Try

conn.Open()

dt = conn.GetOleDbSchemaTable(OleDbSchemaGuid.Columns, New Object() {Nothing, Nothing, TableName, Nothing})

Catch ex As Exception

Throw ex

End Try

For i As Integer = 0 To dt.Rows.Count - 1

Dim ColName = dt.Rows(i)("Column_Name").ToString().Trim()

ColList.Add(ColName)

Next

End Using

Return ColList

End Function

End Class

VB中的EXP函數(shù)

exp(arg) 表示自然對數(shù) e的arg次方,e≈2.71828182845905因此exp(1)就是e的一次方,以此類推exp(0)=1exp(-1)=0.367879441171442exp(-2)=0.135335283236613

VB語言,EXP數(shù)字函數(shù):返回以e底,以X為指數(shù)的值

exp(3)=e^3

e=2.718281828459045.....

e是個超越數(shù)，和圓周率pi類似，具體解說可以百度

exp(n)就是求這個數(shù)的n次方

例子

' 求e^13

Dim a as Double

a = exp(13)

文章標題：vb.netexp的簡單介紹
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