Some remarks about your corrections:

• we are using IF (exist($dirs[$i]) = 1)
  instead of IF (exist($dirs[$i]+$files[$k]) = 1)
  for situations the directory
  $dirs[$i]
  doesn't contain the file
  $files[$k]
  but this file can be located in a subdirectory.
  it isn't necessary to run the dir command
  when the $dirs[$i] directory doesn't exist.
  
• the result of exist function is an integer.
  our advise is
  IF (exist($dirs[$i]) = 1)
  ENDIF
  instead of
  IF (exist($dirs[$i]) = "1")
  ENDIF
  

Greetings.