In ADO.Net, iterating over a loop inside a sql connection is causing error - sql

Question

I am writing a program to maintain an inventory of medicine in our store.
I have a Add to cart list, which opens up the SQL connection and delete 1 quantity from the entire stock where the parameter is #medicine
My addToCart listBox's code looks like this
using (SqlConnection conn = new SqlConnection(cstring))
{
using(SqlCommand cmd = new SqlCommand("Update Medicine set Quantity = Quantity - 1 where Name = #medicine", conn))
{
conn.Open();
foreach(string item in cartMedicine)
{
cmd.Parameters.AddWithValue("#medicine", item);
cmd.ExecuteNonQuery();
}
conn.Close();
listMedicine.Items.Clear();
}
}
Now I want to loop my cartMedicine list to get all the names stored in the listbox one by one. But I am getting the error message that,
The variable name '#medicine' has already been declared. Variable names
must be unique within a query batch or stored procedure.'
How can I use the same logic of giving an Adhoc statement each time for each inventory in my Item's list?

Answer 1

Don't add the parameter over and over again but add it once and then just set its value. "AddWithValue is Evil" anyway.
...
SqlParameter sqlParameter = cmd.Parameters.Add("#medicine", SqlDbType.<data type>, <length>)
foreach (string item in cartMedicine)
{
sqlParameter.Value = item;
cmd.ExecuteNonQuery();
}
...
Replace <data type> and <length> with the proper values for the data type of medicine.quantity in the database.