Currency conversion in action.
Introduction
This article describes a simple aspx page that displays prices in multiple currencies, using 'live' exchange rates. The exchange rates used are pulled from a public domain source that is updated daily. The page uses in-line code - so no DLL to distribute.
Background
When I started selling my own software, I wanted to make buying it as painless as possible. I also wanted to appeal to everyone who came to my web site - and not make potential customers reach for the calculator, just because they don't live in my country. I'm always surprised how many web sites still display their prices in one currency - usually US dollars.
At first, I thought PayPal would provide an answer as it has international features. Unfortunately, PayPal only supports a limited number of currencies, and there's a charge for currency conversions. If your native currency is non-US, and your largest market is the US, it can soon add up.
Instead, I decided to display an approximate price in the customer’s currency, along side the native-currency price. Then the customer knows roughly how much they were going to pay, but the transaction happens in the native currency, so no conversion charge.
Converting prices on the fly is easy, but I wanted the exchange rates to be dynamic.
There are several providers of exchange rates, but all the electronic feeds I could find needed to be paid for – and it seemed a lot for a number! I found articles on using Yahoo Finance’s RSS feed, but again, the legal small print made me nervous. There’s even a Code Project article on converting emails from XE.com, but I wanted something simpler.
This article describes my solution – pulling exchange rate information from a public-domain document at the European Central Bank, which is updated daily.
I’ve used the technique on my web site and it works well.
Enjoy!
Using the code
The sample page PricingDemo.aspx displays base prices and a combo box of currencies. Select a different currency and submit the page. The getConversionRate function looks up an exchange rate for the currency. The PrintPrice function returns a string containing the base price and the price in the selected currency.
To use the code on your page, copy the following block into your page:
<script language="VB" runat="server">
Public Function getConversionRate(ByVal sFromCurr _
As String, ByVal sToCurr As String) As Double
Dim req As HttpWebRequest
Dim res As HttpWebResponse
Dim srExRateData As StreamReader
Dim sExRateData As String
Dim separator As Char() = ","
Dim dRate = 0, dRate1, dRate2 As Double
Dim oExRateData As System.Xml.XmlDocument
Const sExRateSource As String = _
"http://www.ecb.int/stats/eurofxref/eurofxref-daily.xml"
Try
oExRateData = New System.Xml.XmlDocument
srExRateData = New _
StreamReader(WebRequest.Create(sExRateSource)_
.GetResponse().GetResponseStream(), _
Encoding.ASCII)
oExRateData.Load(srExRateData)
srExRateData.Close()
dRate1 = getEuroRate(oExRateData, sFromCurr)
dRate2 = getEuroRate(oExRateData, sToCurr)
dRate = dRate2 / dRate1
Catch
End Try
Return dRate
End Function
Function getEuroRate(ByRef oExRateData As _
System.Xml.XmlDocument, ByVal sCurr As String) As Double
Dim oExRateNode As System.Xml.XmlNode
oExRateNode = oExRateData.SelectSingleNode("*/*/*/*[@currency='"_
+ sCurr + "']/@rate")
If Not oExRateNode Is Nothing Then
Return CDbl(oExRateNode.Value)
Else
Return 1
End If
End Function
Public Function PrintPrice(ByVal dPrice As Double, _
ByVal dRate As Double, ByVal sCurr As String) As String
Dim sReturn as string
if sCurr="USD" then sCurr="$US"
if not sCurr="" then
sReturn = (dRate * dPrice).ToString("#") & sCurr & "<sup>*</sup> "
end if
sReturn += "GB£" & dPrice
return sReturn
End Function
</script>
<%
'Initialise exchange rates
Dim sCurr as string ="USD" 'Default currency
Dim oReqCurr as object =request("curr")
if not oReqCurr is nothing then sCurr=oReqCurrr
Dim dRate = getConversionRate("GBP",sCurr)
Dim Price1 as string ="25.00"
Dim Price2 as string ="75.00"
'End of initialisation
%>
Add the Change Currency combo and button by pasting the following into your page and changing the action of the FORM tag to point to that page.
<form method="post" action="ThisPage.aspx">
<sup>*</sup> Approximate prices in my currency <br>
<select name="curr">
<option value="">Select Currency...</option>
<Option Value="USD">US Dollar</Option>
<Option Value="EUR">Euro</Option>
<Option Value="JPY">Japanese Yen</Option>
<Option Value="DKK">Danish Krone</Option>
<Option Value="GBP">Pound Sterling</Option>
<Option Value="SEK">Swedish Krona</Option>
<Option Value="CHF">Swiss Franc</Option>
<Option Value="ISK">Icelandic Krona</Option>
<Option Value="NOK">Norwegian Krone</Option>
<Option Value="BGN">Bulgarian Lev</Option>
<Option Value="CYP">Cyprus Pound</Option>
<Option Value="CZK">Czech Koruna</Option>
<Option Value="EEK">Estonian Kroon</Option>
<Option Value="HUF">Hungarian Forint</Option>
<Option Value="LTL">Lithuanian Litas</Option>
<Option Value="LVL">Latvian Lats</Option>
<Option Value="MTL">Maltese Lira</Option>
<Option Value="PLN">Polish Zloty</Option>
<Option Value="ROL">Romanian Leu</Option>
<Option Value="SIT">Slovenian Tolar</Option>
<Option Value="SKK">Slovakian Koruna</Option>
<Option Value="TRY">New Turkish Lira</Option>
<Option Value="AUD">Australian Dollar</Option>
<Option Value="CAD">Canadian Dollar</Option>
<Option Value="HKD">Hong Kong Dollar</Option>
<Option Value="NZD">New Zealand Dollar</Option>
<Option Value="SGD">Singapore Dollar</Option>
<Option Value="KRW">South Korean Won</Option>
<Option Value="ZAR">South African Rand</Option>
</select>
<input type="submit" value="Change Currency" name="cmdChange">
</form>
Display a price using:
<%=PrintPrice(Price1,dRate,sCurr)%>
To add a PayPal button, use code like this:
<form target="paypal"
action="https://www.paypal.com/cgi-bin/webscr" method="post">
<input type="image"
src="https://www.paypal.com/en_GB/i/btn/x-click-but22.gif"
border="0" name="submit"
alt="Make payments with PayPal - it's fast, free and secure!">
<input type="hidden" name="add" value="1">
<input type="hidden" name="cmd" value="_cart">
<input type="hidden" name="business" value="<<<your PayPal email address>>>">
<input type="hidden" name="item_name" value="<<Product Name>>">
<input type="hidden" name="item_number" value="<<<Product Code>>>">
<input type="hidden" name="amount" value="<%=GFLitePrice%>">
<input type="hidden" name="no_note" value="1">
<input type="hidden" name="currency_code" value="GBP">
</form>
Obviously, you can customise PrintPrice as you need.
How It Works
The page uses the European Central Bank’s daily exchange rate data, which is published in XML here.
The data set contains conversion rates from Euros. To convert, say, British Pounds to US Dollars, the getConversionRate function simply looks up the rate for Euros to Pounds, and the rate for Euros to Dollars, using getEuroRate. If you happen to be converting to or from Euros, getEuroRate returns 1, so one or other of the rates is ignored.
Missing Classic ASP?
ASP.NET is great, but sometimes, I pine for ASP classic. There’s something nice about being able to write a page without having to worry about compiling a DLL and uploading it, so I decided to use in-line code. There doesn’t seem to be much documentation on in-line code in aspx, but it’s easy.
The main ‘tricks’ are:
- Declare your functions in a
<script language="VB" runat="server"> </script> block.
- Use
<% ...... %> tags to insert code into the HTML, just like classic ASP.
- To get information posted from forms, use constructs like:
Dim oReqCurr as object =request("curr")
More To Do
I don't like the idea that my web page won't show prices because the ECB website's thrown a tantrum. So I want to amend the code so that the XML is cached locally, and only updated if it’s a day out of date.
Your Comments Please
This is my first CodeProject article, and I'd appreciate your feedback. Good? Bad? Interesting? Useful? Made you laugh? Made you cry? Let me know please...
