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Fortran Blog Post
program debt_prioritizer
implicit none
type debtor
character(len=:), allocatable :: name
integer :: debt
end type debtor
! Ugh! Global variables!?
! Originally, I was passing the "debtors" and "debtor_count"
! variables as parameters to all the subroutines and functions.
type(debtor), dimension(:), allocatable :: debtors
integer :: debtor_count = 0
call assign_values_to_globals()
call prioritize_debt()
contains
! Assigns values to the global variables declared at the start of the
! program.
subroutine assign_values_to_globals()
call assign_debtor_count(debtor_count)
allocate(debtors(debtor_count))
call assign_debtors()
end subroutine assign_values_to_globals
! Loops through the file to determine how many people owe money.
! I know this seems stupid to open the file twice, but I
! couldn't find a way to dynamically allocate items to an array
! that I could actually understand.
subroutine assign_debtor_count(debtor_count)
integer :: debtor_count, read_status, sum_of_lines = 0
! Open the input data file for reading:
open(10, file = "input.txt", status = "old", action = "read")
! Loop through each line in the file to get a running count:
do
! The "iostat" is used for error handling. If there's nothing to
! read, it throws an error (which is just a number other than 0).
! We don't want it to throw an error though, because it just hit
! the end of the file.
read(10, *, iostat = read_status)
if (read_status /= 0) exit
sum_of_lines = (sum_of_lines + 1)
end do
! If you don't do this, you end up with a crazy big number:
close(10)
debtor_count = sum_of_lines
end subroutine assign_debtor_count
! Opens the input file, loops through the records, and populates the
! debtors array with the name and debt of the corresponding debtor.
subroutine assign_debtors()
character(50) :: line, name
integer :: read_status, debt, line_number = 1
! Open the input data file for reading:
open(10, file = "input.txt", status = "old", action = "read")
! Loop through each line in the file to get the name and debt:
do
read(10, "(A)", iostat = read_status) line
! Exit the loop at the end of the file:
if (read_status /= 0) exit
! Populate the name and debt variables with the value
! from the input file:
call get_name_and_debt(line, name, debt)
debtors(line_number)%name = name
debtors(line_number)%debt = debt
! There needs to be an iterator to assign to each debtor:
line_number = (line_number + 1)
end do
close(10)
end subroutine assign_debtors
! Once the debtors are loaded into the array and their debt is calculated,
! this reorders them descending by debt (so whoever owes the
! most money is right at the top of the list). Once that's done, the
! debtors are written to a CSV file for easy parsing!
subroutine prioritize_debt()
call sort_descending_by_debt()
call write_debtors_to_file()
print *, "Done!"
end subroutine prioritize_debt
! Splits the value of the line into the person's name and their
! corresponding debt.
subroutine get_name_and_debt(line, name, debt)
! The name and debt in the input file are separated by a pipe:
character(1) :: DELIM = "|"
character(50) :: line, name, debt_string
integer :: debt, index
! Get rid of any whitespace at the end of the line:
line = trim(line)
! Get the position of the pipe character:
index = scan(line, DELIM)
! Pull the name from the line, essentially this grabs the line value
! from the first character of the line to where the pipe character was
! found in the "scan" function above:
name = line(1 : index - 1)
! Pull the debt from the line, this just grabs the line value from the
! first character after the pipe until the end of the line:
debt_string = line(index + 1 : )
! Convert the debt to a number. Character strings are
! considered to be "internal files" in Fortran.
! See https://www.eng-tips.com/viewthread.cfm?qid=37205
read(debt_string, '(I5)') debt
end subroutine get_name_and_debt
! This is a ridiculously inefficient bubble sort. It loops through each
! record, and within that loop it does another loop The higher debt
! amount is moved before the lower debt amount. This has to be done for
! each record, which is why there are 2 loops.
subroutine sort_descending_by_debt()
integer :: base_index, compare_index
! This loop starts at the beginning of the list and iterates by 1:
do base_index = 1, debtor_count
! This loops through each record in the file (starting from the
! bottom of the list), looks at the value of the debt, and either
! leaves it in it's current position (if lower than the parent
! value) or moves it after the parent value:
do compare_index = debtor_count, (base_index + 1), -1
call swap(debtors(compare_index - 1), debtors(compare_index))
end do
end do
end subroutine sort_descending_by_debt
! Given two debtors, this reorders them descending by debt level. If the
! larger debt value is on the left side, it doesn't do anything.
subroutine swap(left_debtor, right_debtor)
type(debtor) :: left_debtor, right_debtor, temp
if (left_debtor%debt < right_debtor%debt) then
temp = right_debtor
right_debtor = left_debtor
left_debtor = temp
end if
end subroutine swap
! If the CSV file "output.csv" doesn't already exist, it creates it in the
! same directory where you compiled the program. Once the file exists, it
! writes each debtor to the file.
subroutine write_debtors_to_file()
character(len=:), allocatable :: name_trimmed
integer :: debtor_number
print *, "Creating the output file..."
open(20, file = "output.csv", action = "write")
! This just writes the first line headers so when you copy it into
! your spreadsheet software, you know what the columns represent:
write (20, "(A)") "Name,Debt"
do i = 1, debtor_count
! Get rid of any extra whitespace in the name:
name_trimmed = trim(debtors(i)%name)
print *, debtors(i)%debt
! Write the name and debt (separated by a comma) to the output file:
write (20, 2000) name_trimmed, ",", debtors(i)%debt
2000 format (A, A1, I5)
end do
close(20)
end subroutine write_debtors_to_file
end program debt_prioritizer
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