Whats wrong with this for and foreach loop logic

This works fine for the first row in the gridview, but on the 2nd it still has the previous values in the variables, so all of 2nd row fail to return / check true
foreach (GridViewRow row in gvReqDetails.Rows) { if (dtOld != null && dtOld.Rows.Count > 0) { for (int i = 0; i < row.Cells.Count; i++) { TextBox txtPart = (TextBox)row.FindControl("txtPartNumber"); currPart = txtPart.Text; oldpartnumber = dtOld.Rows[i][2].ToString(); if (currPart != oldpartnumber) { }