Shift register driven by pic16f627a

Hey guys, i really need help. I'm suppose to write a program that; on two displays; counts up and down<0-to-99> depending on the state of switch. it works when I call the look-up table but now we're told not to use the look up table at all. I'd really appreciate a starting point

make two digit BCD counter then send the values to your shift registers on any change.