anchor.diff:  
   WRITE(*,'(1X,A)') 'Input file :'
   READ (*,'(A)')  INFIL
  -OPEN(UNIT=10,FILE=INFIL,ERR=5000,STATUS='OLD')
  +OPEN(UNIT=10,FILE=INFIL,STATUS='OLD')
   
   ! Open new output file
   
   WRITE(*,'(1X,A)') 'Output File'
   READ (*,'(A)') OUTFIL
   
  -OPEN(UNIT=11,FILE=OUTFIL,ERR=6000,STATUS='NEW')
  +OPEN(UNIT=11,FILE=OUTFIL,STATUS='NEW')
   
   
   ! Get the number hydration spheres to add to each existing sphere from user
   WRITE(*,'(1X,A)') 'How many spheres [1,7,13,19,27 Recomended]'
   READ (*,'(I2)') NOOFSPHERES
   
  -IF (NOOFSPHERES .EQ. NULL) THEN
  +IF (NOOFSPHERES .GT. 27 .OR. NOOFSPHERES .LT. 1) THEN
       WRITE (*,'(1X,A)') 'Default set to [1]: '
   ENDIF
   
  
positive.code: 
  END DO
  
  CLOSE (UNIT=10)
  CLOSE (UNIT=11)
  STOP 'Finished !'
  
  END PROGRAM
  
negative.code: PROGRAM hypro
  
  IMPLICIT NONE
  
  ! A program adapted from hydrate to give a shell of spheres
  ! around a brktos sphere file
  