[redhead]

Pseudocode

if(!(array_size%4)) /* ensure we can shift 4 items on each run */
  store array[array_size -3] in temp_1
  store array[array_size -2] in temp_2
  store array[array_size -1] in temp_3
  store array[array_size] in temp_4
  while(array[index])
    switch array[index] with temp_1
    switch array[index+1] with temp_2
    switch array[index+2] with temp_3
    switch array[index+3] with temp_4
    index+=4

And you couldn't think of that yourself ?

By the way, what is old C++ ?? you've got the STL right there, why not use it??