Find all two digit-numbers N such that N+2 is also a two-digit number and the digit sum of N+2 is less than the digit sum of N

Can easily be achived using a simple program, but why?

[b]int[/b] = [b]10[/b]
 while ([b]int[/b] < [b]97[/b]){
    if (mod [b]int[/b],[b]10[/b] + [[b]int[/b] - mod [b]int[/b],[b]10[/b]]){
    add [b]int[/b] to [b]array[/b]
   }
 }