Force ASP.NET textbox to display currency with $ sign

// directive
using System.Globalization;

// code
decimal input = -1;
if (decimal.TryParse(txtUserInput.Text, NumberStyles.Currency,
    CultureInfo.InvariantCulture, out input))
{
    parameter = input.ToString();
}

decimal sValue = decimal.Parse(txtboxValue.Text.Trim());
// Put Code to check whether the $ sign already exist or not.
//Try making a function returning boolean
//if Dollar sign not available do this
{ string LableText = string.Format("{0:c}", sValue); }
else
{ string LableText = Convert.ToString(sValue); }

string sValue = Convert.ToString(txtboxValue.Text.Trim());
// Put Code to check whether the $ sign already exist or not.
//Try making a function returning boolean
//if Dollar sign not available do this
{ string LableText = string.Format("{0:c}", "sValue"); }
else
{ string LableText = Convert.ToString(sValue); }

string value = text_box_to_validate.Text;

string myPattern = @"^$(d{1,3},?(d{3},?)*d{3}(.d{0,2})|d{1,3}(.d{2})|.d{2})$";
Regex r = new Regex(myPattern);
Match m = r.Match(value);

if (m.Success)
{
    //do something -- everything passed
}
else
{
    //did not match
    //could check if number is good, but is just missing $ in front
}