title: Calculate total from datagridview into textbox
body: <p>i have a datagridview which are used to display a transaction record.
  And one of the columns in datagridview is "Total", which is "SubTotal" times with "Quantity". </p>
  
  <p>My question is, how do i gonna make "GrandTotal" by calculating all "Total" in datagridview into textbox?</p>
  
  <p>Here is the screenshot:</p>
  
  <p><img src="https://i.stack.imgur.com/2okNB.png" alt="enter image description here"></p>
  
  <p>if you see in the datagridview above, there is column named "Total", this "Total" was got from "Quantity" times "SubTotal", what i want is i want to calculate the "Total" (Sum all of the "Total" in the column) into textbox.</p>
  
  <p>How do i gonna do that?</p>
  
  <p>I already thought about it, but i cannot came with an idea how do i calculate (sum) the "Total" column in the datagridview into the textbox.</p>
  
  <p>I appreciate your answer.
  Thank you very much!</p>