Encode URL

/// <summary>
/// Encodes an URL
/// </summary>
/// <param name="str">Input URL</param>
/// <returns>Returns an encoded URL</returns>
public static string Encode(string str)
{
    StringBuilder b = new StringBuilder();

    foreach (Char c in str)
    {
        int decValue = (int)c;

        //Exclude Unreserved Characters (RFC 3986)
        if ((decValue >= 48 && decValue <= 57) || // 0 - 9
            (decValue >= 65 && decValue <= 90) || // A - Z
            (decValue >= 97 && decValue <= 122) || // a - z
            decValue == 45 || // -
            decValue == 95 || // _
            decValue == 46 || // .
            decValue == 126) // ~
        {
            b.Append(c);
        }
        else
        {
            b.Append("%" + decValue.ToString("X"));
        }
    }

    return b.ToString();
}