Disk I/O

References: Section 10 Fortran95 Manual and the Fortran Lecture5

 

            In READ/WRITE statements, unit can be an integer number, which is assigned to a file by using the OPEN statement. The general form for disk I/O is:

 

    OPEN ( [UNIT=] unit,  FILE = file_name  [, specifiers])

    READ ( unit, format [, options] ) variable_list

    WRITE ( unit, format [, options] ) list

    CLOSE ( [UNIT=] unit [, STATUS = status])

 

            For example, the following program read real numbers from keyboard and save those numbers in file fred.DAT (fred.DAT is a new file, which doesn’t exit on the disk).

     PROGRAM NEWDATAFILE

     OPEN (UNIT=14,FILE=’fred.DAT’, STATUS=’NEW’)

                                   ! open fred.DAT and link it to unit=14

     WRITE (*,*)  ‘ TYPE IN A LIST OF REAL NUMBERS,ENDING WITH A LETTER’

100  READ (*,1000,ERR=101)X        ! input from keyboard

     WRITE (*,1000) X              ! output to monitor screen

     WRITE (14,1000) X             ! output to fred.DAT

     GOTO 100

101  CLOSE(14)                     ! close fred.DAT

1000 FORMAT (F12.3)

     END

 

Exercises  

1) A unit number is an integer number. What is the range of the unit number?

2) What will happen, if fred.DAT already exists on the disk?

3) (optional) Write a program (fred_r.f95) to read data from fred.DAT and calculate the sum of all the numbers.

4) Use a text editor to create a data file (input.dat) containing the following 10 numbers.

            0.96     0.95     9.51     9.54     10.10

            11.45   0.95     12.34   31.4     11.08

'input.dat' should have 10 lines with one data on each line.

 

    Write a program (diskIO.f95) to read data in 'input.dat' and find out how many numbers are below the average among the 10 numbers. Print the result on the screen.

    Sort the 10 numbers in numerical order starting with the smallest and save the sorted 10 numbers onto a file (output.dat).