!Name: Nicholas Farkash
!Purpose: Process an arbitrarily large set of real data from a file,compute
!         the arithetic mean, median, and standard deviation of the data set,
!         and write data to a file.
!Date: October 27th, 2021
!Due: November 1st, 2021 at 6:00PM

program HW_9
  implicit none

  character(len=100) :: bufferread           !File name for data input
  character(len=:),allocatable :: fnamein    !Trimmed version of name

  integer :: lun                !LUN for referencing other files
  integer :: ierror=0           !I/O erorr check

  real :: x                     !Variable to read in data points
  integer :: npts               !Number of data points read in

  real, allocatable :: a(:)     !Allocatable array of unspecified dim.

  integer :: i                  !Loop variable
 
  real :: sumavg                !Sum while calculating the average
  real :: avg                   !Average of the data points

  real :: med                   !Median of the data points
  
  real :: sumstdv               !Sum while calculating the standard deviation
  real :: stdv                  !Standard deviation of the data points

  integer :: j                  !Loop variable
  integer :: smallpos           !Position of the smallest value of array
  real :: temp                  !Placeholder variable for swap during sort

  character(len=100) :: bufferwrite           !File name for data output
  character(len=:),allocatable :: fnameout    !Trimmed version of name

  
  
  write(*,*) "Enter file name to read data from:"
  read(*,*) bufferread                   !Read in the file for data input
  fnamein = trim(bufferread)             !Trim the name to use in program

  
  open(newunit=lun,file=fnamein,status="old",iostat=ierror,action="read")
   if(ierror /= 0)then
      write(*,*) "Data failed to open!"         !Check to see if file can
      stop 1                                    !be opened safely. If so,
   endif                                        !open the file

   
   do while (ierror == 0)                       
      read(lun,*,iostat=ierror) x               !Read in the data from 
      if(ierror == 0) then                      !the specified file
         npts = npts+1
      else
         exit
      endif
   enddo


   allocate(a(npts))   !Set the length of array a equal to
   rewind(lun)         !the number of data points read in

   
  write(*,*) "The number of points in this file is",npts

  
  do i=1,npts
     read(lun,*) a(i)  !Read in the entire array
  enddo

  
  close(unit=lun)      !Close the file being read from.


  sumavg = 0.0e0
  do i=1,npts
     sumavg = sumavg + a(i)     !Calculate the mean of the data points
  enddo
  avg = sumavg / npts

  
  write(*,*) "The arithmetic mean of these values is",avg


  if ( (-1.0)**npts < 0.0) then    !Determine whether the array has an even or odd
     med = a((npts+1)/2)           !number of data points. Then calculate the
  else                             !median value of the array
     med = (a(npts/2) + a(npts/2 + 1)) / 2.0e0
  endif

  
     write(*,*) "The median of these values is",med

     
  sumstdv = 0.0e0
  do i=1,npts
     sumstdv = sumstdv + ( a(i) - avg )**2   !Calculate the standard deviation of 
  enddo                                      !the data points
  stdv = sqrt(sumstdv / npts)

  
  write(*,*) "The standard deviation of these values is",stdv

  
  do j=1,npts-1
     smallpos = j          !Assume the first position holds the smallest value     

     do i=j+1,npts
        if ( a(i) < a(smallpos)) then     !If another value has a smaller value,
           smallpos = i                   !make it the new smallest
        endif
     enddo

     temp = a(j)                  !Set the placeholder variable equal to the first unsorted value
     a(j) = a(smallpos)           !Set the first value of the Sorted Array to the new smallest value
     a(smallpos) = temp           !Replace the first unsorted value. This process swaps the locations.

  enddo
  

  write(*,*) "Enter file name to write sorted data to:"
  read(*,*) bufferwrite                 !Read in the file for data input
  fnameout = trim(bufferwrite)          !Trim the name to use in program


  open(newunit=lun,file=fnameout,status="new",iostat=ierror,action="write")  
   if(ierror /= 0)then
      write(*,*) "Data failed to write!"         !Check to see if file can
      stop 1                                     !be opened safely. If so,
   endif                                         !open the file

   
   
  do j=1,npts
     write(lun,*) j,a(j)         !Write the data to the specified file                
  enddo

  
  close(unit=lun)                !Close the file being written to

  
  deallocate(a)                  !Deallocate the space for the array

  
  stop 0
end program HW_9