Problem alter add column using asp.net and vb.net

[Eniekko]

hello to all. I have a problem. I want to alter a table to add three columns whenever i click a button.But i want the name of the table taken from a drop down list, and the name of the three columns are also taken from either a drop down list or a textbox. Here's the code that i used as trial for the first column:

con.Open()
        cmd = New SqlCommand("ALTER TABLE " + ddl_sub.Text + " ADD " + txt_desc.Text + " varchar(50) ", con)
        cmd.CommandType = CommandType.Text
        cmd.ExecuteNonQuery()
        con.Close()

However, when i try it, it say "incorrect syntax near varchar" and when i add (') the error becomes "incorrect syntax near 'quiz'". If i change it back, the code works but if i click the button again, "incorrect syntax near varchar" appears again... Help please.. Is my code wrong? i'm new at this. By the way im making use of sql server

[hericles]

You are missing the keyword COLUMN:

cmd = New SqlCommand("ALTER TABLE " + ddl_sub.Text + " ADD COLUMN " + txt_desc.Text + " varchar(50) ", con)

[Eniekko]

well, thanks for the reply. but when i tried adding the word COLUMN, it still showed an error..

There's this part from my code

Page.Response.Redirect("myform.aspx")

when i tried removing it, my code as it is, actually worked. I don't know if the redirect code has got anything to do with it but now its working.

Thanks a lot though :)