我正在尝试使用C#更改表添加列

我想使用C#以编程方式向SQL表中添加列。 这是我的代码。

SqlConnection con = new SqlConnection(conString);
con.Open();
string str = "ALTER TABLE  [dbo].[tblQuiz] ADD '" + txtQuizNo.Text.ToString() +"' Varchar(50) NULL ";
SqlCommand com = new SqlCommand(str, con);
com.ExecuteNonQuery();
con.Close();

When I execute the program it say's that Incorrect syntax near the column nameenter code here. Is it possible to add column to the sql database programmatically?