Windows Batch, 204
set a=0
:a
set /p i=^>^>
if %i%==i set a=%a%+1
if %i%==x set a=%a%+1
if %i%==d set a=%a%-1
if %i%==s set a=%a%*%a%
if %i%==k set a=%a%*%a%
if %i%==o echo %a%
if %i%==c echo %a%
if %a%==256 set a=0
goto a
Successfully ignores other commands. Really got bloated without having or to work with...