C # Learning (01) string to 16 binary

Private byte[] string2hex (string stmp) {    stringbuilder sbtmp =  new stringbuilder ();    for  (int i = 0; i <  stmp. length; i++)     {        if  (Stmp[i]  >=  ' 0 '  && stmp[i] <=  ' 9 ')          {            sbtmp. Append (Stmp[i]);        }         else if  (stmp[i] >=  ' a '  && stmp[i] <=  ' F ')          {             sbtmp. Append (Stmp[i]);        }         else if  (Stmp[i] >=  ' A '  && stmp[i] <=  ' F ')          {            sbtmp. Append (Stmp[i]);        }    }     if  (sbtmp. length % 2 != 0)          sbtmp. Append (' 0 ');     byte[] btmp = new byte[sbtmp. length/2];    byte l,h;    for  (int i = 0,j  = 2; i < sbtmp. Length;)     {        h = char2hex (sbtmp[ I]);         i++;        if (i  >= sbtmp. Length)             break; &nbsP;      l = char2hex (Sbtmp[i]);         i++;        btmp[i-j] =  (Byte) (h*0x10+l);         j++;    }             return btmp;} Private byte char2hex (char s) {    if  (s >=  ' 0 '  & & s <=  ' 9 ')     {         return  (Byte) (s - 0x30);    }    else if  (s  >=  ' a '  && s <=  ' F ')     {         return  (Byte) (s - 0x57);    }     else if  (s >=  ' A '  && s <=  ' F ')     {        return  (byte) (s - &NBSP;0X37);    }    else    {          return 0;    }}

C # Learning (01) string to 16 binary