At least one element in the source array could not be cast down to the destination array type.

public void no()
{
    SqlCommand cmd = new SqlCommand("select qno from QUIZ1 where applicationname = @appname", con);
    cmd.Parameters.AddWithValue("@appname", this.application);
    con.Open();
    ArrayList al = new ArrayList();
    SqlDataReader sdr = cmd.ExecuteReader();
    while (sdr.Read())
    {
        object[] values = new object[sdr.FieldCount];
        sdr.GetValues(values);
        al.Add(values);
    }
            
   this.str = ((int[])al.ToArray(typeof(int)));
}