my @string = split //, "ABCDEFGHIJKL";
my $spalten = 5;
$spalten--;
foreach my $offset (0..$spalten) {
        foreach my $zeile (0 .. @string/$spalten) {
                my $wert = $spalten*$zeile+$offset;
                print $string[$wert] if($string[$wert]);
        }
}

void coder_step2(char* in, char* out, int shift) {
  char* in_p = in; char* out_p = out;
  int len = strlen(in) + 1;
  int i;
  for(i = 0; i < len; i++) {
    char c = *(in_p + (i*shift)%len);
    if(c != '\0') 
      *(out_p++) = c;
  }
  *out_p = '\0';
}

void coder_step2(char* in, char* out, int shift) {
  for(int i = 0, len = strlen(in) + 1; i < len; i++) {
    char c = in[(i * shift) % len];
    if(c)
      *(out++) = c;
  }
  *out = 0;
}