0-99 counter using one port ATMega32

Question

How to count from 0 to 99 using two 7SEG-BCD in proteus. I also tried to shift bits but i didn't succeed.

$regfile="m32def.dat"
$crystal=8000000

config portc = output

dim a as byte,b as byte

do

  for a = 0 to 9
      for b = 0 to 9
         portc = makeint(a, b)
         waitms 100
      next
  next

loop
end