Data Controls :: Compare Values Of Each Row In GridView And Show Alert If Value Is Maximum Than Previous Value

How to check the condition  if the input QTy is more than current Qty then pop up the message?

 For the example, if the input adjQty is more that  Data key of Values Qty , then pop up  alert meesage .

protected void gvAdjQty_RowUpdating(object sender, GridViewUpdateEventArgs e) {
SqlConnection conC = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings
["CIMProRPT01testserverConnectionString"].ConnectionString);
string InvID = gvAdjQty.DataKeys[e.RowIndex].Values["INV_ID"].ToString();
string InvLoction = gvAdjQty.DataKeys[e.RowIndex].Values["INV_LOCATION"].ToString();
string InvQty = gvAdjQty.DataKeys[e.RowIndex].Values["INV_QTY"].ToString();
TextBox Inv_AdjQty = (TextBox)gvAdjQty.Rows[e.RowIndex].FindControl("Inv_AdjQty");