How to assign value to datagrid column

Hello Everyone,

        I got an employee_Works table with columns eid,ename,sdate,edate,wages/day.Now I need to calculate his salary based on sdate and edate. Below are the steps what I followed :
         In addition to the other columns i added a boundfiled to gridview manually for salary because it's not a column in this table.I am not sure whether i can do it manually or not.Now I calculated the difference between the dates.

            DateTime d1 = DateTime.Parse(sdate);
           DateTime d2 = DateTime.Parse(edate);
           TimeSpan ds = d2 -d1;DateTime d1 = DateTime.Parse(sdate);
           DateTime d2 = DateTime.Parse(edate);
           TimeSpan ds = d2 -d1;

            float sal = ds * wages;

Now I need to assign this value to the grid view for Salary cell.Let me know how to proceed?

Hello,

      I wrote the below query:

          DateTime d1 = DateTime.Parse(sdate);
           DateTime d2 = DateTime.Parse(edate);
           TimeSpan ds = d2 -d1;DateTime d1 = DateTime.Parse(sdate);
           DateTime d2 = DateTime.Parse(edate);
           TimeSpan ds = d2 -d1;

    select emp_id,emp_name,sdate,edate,wages,wages * ds as SAL from employee_Works;

What is wrong with this query getting an error invalid identifier at ds.

and trying to assign the value ds to the grid view.

grdView.Rows[3].Cells[3].Text = SAL;

Getting an error index out of range. Must be non-negative and less than size of collection.

Regards.