append date column to datatable and add days based on another column

Question

I need to append a column to datatable in c# , like the folowing , (endofregistration) is the column that should be added , it should be datetime.now.adddays(value from another column example [5]) . my code is able to perform right only for the first row when in debug mode , then all the values of the appended column are taking the values of the last value[4]. example :

endofregistreation | id | price | orderdate  |days 
28/02/2022          1     50      18/02/2022  10     ----> this is the correct result 

endofregistreation | id | price | orderdate  |days 
18/02/2023          1     50      18/02/2022  365     ----> this is the correct result 

after running my code, all the rows values will be calculated based on the last value read from days column which is not correct...

below is my code:

using (SqlCommand cmdbindertables = new SqlCommand("SELECT from the table", con))
{
    cmdbindertables.CommandType = CommandType.Text;

    using (SqlDataAdapter sda = new SqlDataAdapter(cmdbindertables))
    {

        sda.Fill(dtperiodlenght);



    }
    DateTime invDate = DateTime.Now;
                          



    foreach (DataRow row in dtperiodlenght.Rows)
    {
        need to set value to New SADERLEX STORE Columns 
        row["CustomerID"] = Session["uid"].ToString();
        row["OrderDate"] = invDate.ToString("dd/MM/yyyy");

    }


    for (int x = 0; x < dtperiodlenght.Rows.Count; x++)
        for (int j = 0; j < dtperiodlenght.Columns.Count; j++)
        {
            object o = dtperiodlenght.Rows[x].ItemArray[j];
            if you want to get the string
            string s = Convert.ToString(o = dtperiodlenght.Rows[x].ItemArray[j]);
            string K = Convert.ToString(o = dtperiodlenght.Rows[x].ItemArray[9]);
            thedaystocount.Text = K;


        }