Record not inserted to Database after Converting string to double using C# in ASP.Net

Name varchar(30),

Single float

Have to textbox in widows form application C#.

I want insert name and single value float, but it’s not save float.

I used below code:

public void adddegr(string nm, double sng)
{
    SqlCommand cmd = con.CreateCommand();
    cmd.CommandText = "insert into People(name, single)values(N'" + nm + "'," + sng + ")";
    con.Open();
    try
    {
        cmd.ExecuteReader();
    }
    catch { }
    con.Close();
}

In button_click

adddegr(name.Text, Convert.ToDouble( single.Text));