Thank you a lot,

two more questions, how to avoid the error message if the user leave the option 0 (<option value="0">Select</option>)? Instead use something like this code, but for the list because i get error:Invalid column name :

var UserInput = Request["UserInput"].AsDecimal();
if (UserInput == 0) {
ModelState.AddError("UserInput", "Enter amount!");
}

and how to display the Result after the submit, (for the code below)

@{
    var db = Database.Open("money");
    var lastRecord = db.QuerySingle("SELECT TOP 1 * FROM foreign ORDER BY ID DESC");
    
    var Result = 0m;
    var LastValue = Request["UserInput"];
    var LastPrice = Request["currency"];
    
    if(IsPost) {
        
    var Price = decimal.Parse(lastRecord[Request["currency"]]);
        
        
    var UserInput = Request["UserInput"].AsDecimal();
        if (UserInput == 0) {
           ModelState.AddError("UserInput", "Enter amount!");
        }
        
    // calculate
    Result = UserInput * Price;
    }
}

    
    
    
    <form action="" method="post">

<table>
    <tr>
        <td><select name="currency">
    <option>Select</option>
    <option>USD</option>
    <option>EUR</option>
    <option>GBP</option>
    <option>CHF</option>
    <option>JPY</option>
</select></td>
        </tr>
    <tr>
        <td><input type="text" name="UserInput" size="14" value="1"/> <input type="submit" value="Go"/></td>
        
    </tr>
</table>
        
     </form>
    
    <text>@if(ModelState.IsValid) {<span>Result:</span> @LastValue<span>&nbsp;</span>@LastPrice @Result} else {@Html.ValidationSummary()}</text>