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copied!<p>The problem stated by your error message is probably on one of the lines that try to convert the value in the textboxes to a short integer. Without any check, the value typed by your user could be anything but a number and you get this error message (for example, if you user leaves the textboxes empty). </p> <p>You should try to check if the textboxes content could be converted to a valid short integer using <a href="http://msdn.microsoft.com/en-us/library/system.int16.tryparse.aspx" rel="nofollow">TryParse</a> before attempting to execute the query</p> <pre><code>int ordered; if(!int16.TryParse(txtQtyOrdered.Text, out ordered)) { MessageBox.Show("Invalid number for Ordered quantity"); return; } int orderID; if(!int16.TryParse(txtPONumber.Text, out orderID)) { MessageBox.Show("Invalid number for OrderId"); return; } int itemID; if(!int16.TryParse(txtItemNo.Text, out itemID)) { MessageBox.Show("Invalid number for ItemID"); return; } </code></pre> <p>At this point you could execute your calculation using the converted short integers and then write your query in this way (adding a space before the AND)</p> <pre><code> com.CommandText = "UPDATE PODetail SET BalanceQty="+ newbal.ToString() + " WHERE OrderID=" + orderID.ToString() + " AND ItemID=" + itemID.ToString(); </code></pre> <p>But the string concatenation of query text and user input is never advised as a good practice (in your case is harmless because if the conversion is successful you don't have to worry about Sql Injection, but don't take the habit to do it).<br> So the perfect way to write this query is through the use of a parametrized query</p> <pre><code> com.CommandText = "UPDATE PODetail SET BalanceQty=@newbal " + " WHERE OrderID=@orderID " + " AND ItemID= @itemID" com.Parameters.AddWithValue("@newbal", newBal); com.Parameters.AddWithValue("@orderID", orderID); com.Parameters.AddWithValue("@itemID", itemID); com.ExecuteNonQuery(); </code></pre> <p>As a good article on Parameterized query and why to use them, I suggest to <a href="http://www.codinghorror.com/blog/2005/04/give-me-parameterized-sql-or-give-me-death.html" rel="nofollow">read these old words</a> from Jeff Atwood</p>

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