1. 11/06/20151 FORTRAN 77 Programming. Lecture 5 : January 2001 Dr. Andrew Paul Myers

2. 11/06/20152 Screen Output. So far the output of results to the screen has been “messy”, because we have been using “free format”. e.g. PRINT*,’Radius = ‘,radius,’ cm’ typical screen output : Radius = 7.2345121cm

3. 11/06/20153 Free Format.  Free format is simple and easy to use. e.g. with the PRINT* and READ* statements.  Assumes numeric input, therefore limited.  Always uses greatest accuracy possible.  Pads out printed variable and text into columns.  Lines that should fit on the screen “wrap around” onto the next line, because of this padding.

4. 11/06/20154 Formatted I/O. The solution to our problem is: Formatted I/O (Input, Output) You have seen formatted input already! READ’(A10)’,character_string

5. 11/06/20155 Formatted I/O. The general form of formatted I/O Statements is as follows: PRINT’( )’, READ’( )’, is a format specifier.

6. 11/06/20156 Format Specifiers. Format specifiers for variables consist of a letter and a digit(s).  A : Character variable.  I : Integer variable.  F : Real variable.  E : Real variable, exponential form.

7. 11/06/20157 Examples. A10 : String variable 10 characters long. e.g. ‘Hello ‘. I8 : Integer, 8 digits long. F6.2 : Real variable, 2 decimal places, 6 digits long including decimal points and minus signs.

8. 11/06/20158 F6.2 again. All these numbers are in F6.2 format. NumberC1C2C3C4C5C6 345.19345.19 1.2 1.20 -23.45-23.45 5 5.00 9999.99******

9. 11/06/20159 Examples. READ’(A30)’,string1 READ’(A30,2I4),string2,num1,num2 PRINT’(“Answer = “,F6.2)’,answer  “ / ” and “ X “ are new line and space. PRINT’(/“A = “,I2,2X,”B = “,F10.1,//)’,a,b PRINT’(“Enter a number “,$)’ READ*,number

10. 11/06/201510 The old way… Formatted I/O the old way, with numeric labels. 100 FORMAT(/’A = ‘,I2,2X,’B = ‘,F10.1//) PRINT 100,a,b 200 FORMAT(3I5) READ 200,int1,int2,int3

11. 11/06/201511 Data Files.  You must first open a data file.  Then read or write data.  Finally close the data file. Data files are analogous to books. Fortran OPEN statement. OPEN(UNIT=x,FILE=y,STATUS=z)

12. 11/06/201512 Opening Data Files. Choose unit numbers >6 Unit 5 = keyboard and Unit 6 = screen! OPEN(UNIT=20,FILE=‘data.dat’,STATUS=‘NEW’) FILE=‘data.dat’ FILE=‘/disk/n/gps/data/data.dat’ FILE=file_name STATUS=‘NEW’ STATUS=‘OLD’ STATUS=‘UNKNOWN’

13. 11/06/201513 Reading and Writing. Once a data file is opened use READ And WRITE statements to access the data file. READ(, ), WRITE(, ),variable(s)>

14. 11/06/201514 File I/O Examples. e.g. READ(1,*) num1,num2,num3 WRITE(20,’(5X,I5,10X,3F5.1)’) a,b,c,d READ(25,’(2F10.5)’) data1(loop),data2(loop)

15. 11/06/201515 Closing a data file. CLOSE(UNIT= | ) CLOSE(UNT=20) CLOSE(20) Close data files when you have finished with them!

16. 11/06/201516 File Pointer. The file pointer is positioned at the beginning of a data file when it is first opened. REWIND(UNIT= | ) Moves the file pointer to the start. REWIND(20) or REWIND(UNIT=20)

17. 11/06/201517 Error Trapping I IOSTAT : Used to test if a file exists if opened with ‘OLD’ or ‘UNKNOWN’ status. e.g. OPEN(IOSTAT=I,UNIT=20, & FILE=‘test.dat’,STATUS=‘OLD’) IOSTAT returns an INTEGER value.

18. 11/06/201518 Error Trapping II. Integer IOSTAT values returned are:  0 : File opened without errors.  >0 : Error, file not found?  <0 : As condition 0, but at end of file (EOF), file empty. What about EOF during reading data?

19. 11/06/201519 Error Trapping III. Using the END option with a READ Statement you can test for EOF. DO WHILE (.NOT. 0 ) READ(25,’(I5)’,END=100 )data(i) END DO 100 CONTINUE