! Based on some depreciation rate(s), this program calculates the depreciated price of 
! a car at the end each year until the depreciated price is the same as or below
! some given price (the final depreciated price). It is assumed that
! depreciation of a car occurs in three different phases. During a phase, the 
! depreciation rate is constant. The last phase (3rd phase) continues for the rest of 
! the life of the car.

! Input file: rate.dat
! 	Line 1:  Original price of the car and the final depreciated price
!       Line 2:  Depreciation rate and years for phase 1
!	Line 3:  Depreciation rate and years for phase 2
!       Line 4:  Depreciation rate for phase 3

! Output file: price.out
!      For each year, the program outputs a line with:
!      year, price, depreciation rate, depreciation, and depreciated value


! Caution: You have to be careful in creating the input file for testing.
! If you type any depreciation rate 0.0 by mistake, the program may never end. 

! Note: Depending on the input data set, the program may not execute all three loops
! to generate output. As soon as the condition for the final depreciated value is met, it
! skips other following loops. That is, not all cars will go through all three phases.

PROGRAM calc_price_depreciation
  IMPLICIT NONE
  REAL :: depreciation_rate_1, depreciation_rate_2, &
          depreciation_rate_3, depreciation, &
          depreciated_price, car_price, final_depreciated_price

  INTEGER :: years_1, years_2, year

  INTEGER :: ios
  INTEGER :: i

  ! Open input file
  OPEN (9, FILE="rate.dat", STATUS ="OLD", IOSTAT=ios)
  IF (.NOT.(ios == 0)) THEN
     WRITE (*,*) "*** Cannot open input file ***"
     STOP
  END IF

  ! Open output file
  OPEN (10, FILE="price.out", STATUS="REPLACE",IOSTAT=ios)
  IF (.NOT.(ios == 0)) THEN
     WRITE (*,*) "*** Cannot open output file ***"
     STOP
  END IF

  ! Read depreciation rates and years 
  READ(9,*,IOSTAT=ios) car_price, final_depreciated_price
  READ(9,*,IOSTAT=ios) depreciation_rate_1, years_1
  READ(9,*,IOSTAT=ios) depreciation_rate_2, years_2
  READ(9,*,IOSTAT=ios) depreciation_rate_3

  IF (ios < 0) THEN
    WRITE(*,*) "*** INSUFFICIENT OR INVALID DATA IN INPUT FILE ***"  
    STOP
  END IF  

! Write heading lines
  WRITE (10,*) "               Depreciation Table"
  WRITE (10,*)
  WRITE (10,*) "Year   Price      %Rate   Depreciation    Depreciated Value"
  WRITE (10,*) "-----------------------------------------------------------" 
 
! Calculations for phase 1 
  i = 0
  year = 0
  DO WHILE (i <  years_1 .AND. car_price > final_depreciated_price)
    depreciation = depreciation_rate_1 * car_price
    i = i + 1
    year = year + 1
    depreciated_price = car_price - depreciation
    WRITE (10, 50) year, car_price, &
        depreciation_rate_1 * 100, depreciation, &
        depreciated_price
    car_price = depreciated_price
  END DO
  

! Calculations for phase 2
  i = 0
  DO WHILE (i < years_2 .AND. car_price > final_depreciated_price)
    depreciation = depreciation_rate_2 * car_price
    i = i + 1
    year = year + 1
    depreciated_price = car_price - depreciation
    WRITE (10, 50) year, car_price, &
        depreciation_rate_2 * 100, depreciation, &
        depreciated_price
    car_price = depreciated_price
  END DO
  
! Calculations for phase 3 
  DO WHILE (car_price > final_depreciated_price)
    depreciation = depreciation_rate_3 * car_price
    year = year + 1
    depreciated_price = car_price - depreciation
    WRITE (10, 50) year, car_price, &
        depreciation_rate_3 * 100, depreciation, &
        depreciated_price
    car_price = depreciated_price
  END DO
   
  CLOSE (9)
  CLOSE (10)
  STOP
50 FORMAT (I5, F10.2, F10.2, F10.2, TR12, F10.2)
END PROGRAM calc_price_depreciation