How to Convert Numeric to data type varchar

Question

 I have field in sql tbl as numeric data type (numeric(18,0) but in c# code when i save data

display this message "

Arithmetic overflow error converting numeric to data type varchar.The statement has been terminated."

 

As follow code c#

 

SqlCommand cmd = new SqlCommand("CashPlan_Insert", Conn);

cmd.Parameters.Add("@CarNo", SqlDbType.VarChar).Value = (DropDownList1.SelectedValue);

cmd.CommandType = CommandType.StoredProcedure;

Conn.Open();

cmd.ExecuteNonQuery();

Conn.Close();