Duplicate random generated numbers

[ljpv14]

Okay I got a situation, I have a code that generates random code using a set of letters. One for a random pin and another for a random code. I can loop the generation of my codes depending on the input. When I try to generate 1 to 3 set of codes it works fine. but if it's 4 and above. I always get a duplicate set of random numbers. I don't what wrong. My code for generating my codes are in vb.net and be passed to a stored procedure for inventory.

Here is my code:

Button event:

Protected Sub genCodeBtn_Click(sender As Object, e As EventArgs) Handles genCodeBtn.Click


        connection = accDB.databaseConnect()
        Dim pin As String = ""
        Dim code As String = ""


        For i As Integer = 1 To CInt(qtyTxtbox.Text)


            pin = generateCode(5, 0)


            code = generateCode(5, 1)


            accDB.accessSp_insert_reg_code(connection, CInt(packCatIdTxtbox.Text), pin, code)


        Next


        MsgBox("Number of affected rows: " + CStr(accDB.getAffectedRows()))


    End Sub

generate code sub:

 Dim keycode As String = ""


        Dim retString As String = ""


        Dim ranvar As Random = New Random()




        If type = 0 Then
            keycode = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890"
        ElseIf type = 1 Then
            keycode = "123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
        End If


        For j As Integer = 0 To len - 1


            retString += keycode(ranvar.Next(keycode.Length - 1))


        Next j


        Return retString


    End Function

databaseConnect method from accessdatabase class:

 Dim connStr As String = ConfigurationManager.ConnectionStrings("Hr_Inventory_Server").ConnectionString


        Dim con As SqlConnection = New SqlConnection(connStr)


        Return con

accessSp_insert_reg_code method in accessdatabase class

 Public Sub accessSp_insert_reg_code(ByVal spConn As SqlConnection, ByVal spPackCatId As Integer, ByVal spPin As String, ByVal spCode As String)
        spConn.Open()


        Dim affectedRows As Integer


        Dim spCmd As SqlCommand = New SqlCommand("sp_insert_reg_code", spConn)


        Dim spParam As SqlParameter = New SqlParameter


        spCmd.CommandType = CommandType.StoredProcedure




        spParam = spCmd.Parameters.Add("@pin", SqlDbType.VarChar)


        spParam.Value = spPin


        spParam = spCmd.Parameters.Add("@code", SqlDbType.VarChar)


        spParam.Value = spCode




        spParam = spCmd.Parameters.Add("@packcatid", SqlDbType.Int)


        spParam.Value = spPackCatId




        affectedRows = spCmd.ExecuteNonQuery()




        setAffectedRows(affectedRows)


        spConn.Close()
    End Sub

I really don't know what causes the duplicates. But I'm pretty sure that my code is right. It's just that at some point when I try to generate 4 or more set of codes. Duplicates begin to arise. Thanks!

PEACE! XD

 

[jmcilhinney]

I've added code formatting tags to your post so that it's readable. Please do so yourself in future.

You're creating multiple Random objects in a loop, which is never a good idea. If you must do that then you should use the constructor that takes a seed and make sure that the seed is unique every time. As it is you are using the system time as a seed which may not have changed sufficiently between iterations to generate a different pseudo-random sequence. Ideally you would use just one Random object, which means using a variable declared outside any methods.