//int转16进制  (long类型同样）
int a=90;
string str= convert.tostring(a,16); //5a

//int转2进制
int a=90;
string str= convert.tostring(a,2); //1011010

//int转byte
int a=90;
string str= Convert.Tobyte(a); //0x5a

//16进制转10
string hex = "5a";
string aa = Convert.ToInt32(hex,16).ToString();// 90

//16进制转2进制
string hex = "5a";
string aa = Convert.ToString(Convert.ToInt32(hex, 16), 2); //1011010
//十六进制字符串转十进制  
     public string ConvertHexToIntStr(string hexstr)
        {
            if (hexstr.StartsWith("0x"))
            {
                hexstr = hexstr.Substring(2);
            }

            //如果不是有效的16进制字符串或者字符串长度大于16或者是空，均返回NULL
            if (!IsHexadecimal(hexstr) || hexstr.Length > 16 || string.IsNullOrEmpty(hexstr))
            {
                return null;
            }
            if (hexstr.Length > 8)
            {
                return Convert.ToInt64(hexstr, 16).ToString();
            }
            else if (hexstr.Length > 4)
            {
                return Convert.ToInt32(hexstr, 16).ToString();
            }
            else
            {
                return Convert.ToInt16(hexstr, 16).ToString();
            }
        }
        // 判断是否是十六进制格式字符串
        public bool IsHexadecimal(string str)
        {
            const string PATTERN = @"[A-Fa-f0-9]+$";
            return System.Text.RegularExpressions.Regex.IsMatch(str, PATTERN);
        }