C# Extension Method for String Data Type

Question

My web application deals with strings that need to be converted to numbers a lot - users often put commas, units (like cm, m, g, kg) and currency symbols in these fields so

Answer 1

Are you expecting users of different 'cultures' to use your application? If so it's better to factor in the user's regional settings:

static decimal ToDecimal(this string str)
{
    return Decimal.Parse(str, CultureInfo.CurrentCulture);
}

Or you could replace every character in str that isn't a digit or the CultureInfo.CurrentCulture.NumberFormat.CurrencyDecimalSeparator value and then parse it as a decimal.

EDIT:
It is generally accepted that extension methods should have their own namespace. This will avoid naming conflicts and force the end user to selectively import the extensions they need.