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LAB-13 File

LAB-13 File. I Putu Danu Raharja raharja @kfupm.edu.sa Information & Computer Science Department CCSE - King Fahd University of Petroleum & Minerals. Background. In real life applications we will handle lots of data The data need to be saved and retrieved for later use

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LAB-13 File

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  1. LAB-13File I Putu Danu Raharja raharja @kfupm.edu.sa Information & Computer Science Department CCSE - King Fahd University of Petroleum & Minerals

  2. Background • In real life applications we will handle lots of data • The data need to be saved and retrieved for later use • It is cumbersome to retype all the data • Use secondary storage → files

  3. Introduction • Standard input is keyboard • Standard output is screen • File is just another input/output device • The operations are similar • READ • WRITE (like PRINT for screen)

  4. Opening a File • Before using a file, it needs to be opened • OPEN (UNIT = INTEXP, FILE = FILENAME, STATUS = STATSTRING) • INTEXP→ the file handle, 0 – 99 (avoid 5 & 6 → keyboard & screen) • FILE→the file name • STATUS→ 'OLD', 'NEW', 'UNKNOWN' • OLD → existing file • NEW → new file; if file exists, it gives error • UNKNOWN → works for existing file or non-existing file • Multiple files can be opened but use different unit numbers

  5. Closing a File • Close a file after no file operation is needed • CLOSE (UNITNO)

  6. Reading from a File • READ (UNITNO, *) VARIABLE LIST • The values are read in similar way with regular READ • The values are stored in the variables in the list

  7. Example 1 – Prepare the Data • Create a file called DATA1.TXT in D:\ using Notepad • Write the contents of the file as follows 10 20 30 • Open the Fortran IDE for the program

  8. Example 1 – The Program INTEGER X, Y, Z OPEN (UNIT = 1, FILE = 'DATA1.TXT', STATUS = 'OLD') READ (1, *) X, Y, Z PRINT*, X, Y, Z CLOSE (1) END

  9. Notes • Change the status into 'NEW' and run the program. What will happen? • Change the status into 'UNKNOWN' and run the program. What will happen?

  10. Writing to a File • WRITE (UNIT, *) VARIABLE LIST • The values are written in similar way with PRINT

  11. Example 2 – The Program INTEGER X, Y, Z OPEN (UNIT = 1, FILE = 'DATA99.TXT', STATUS = 'NEW') X = 50 Y = 60 Z = 70 WRITE (1, *) X, Y, Z CLOSE (1) END

  12. Notes • Change the file name into 'DATA3.TXT' and the status into 'OLD' and run the program. What will happen? • Change the status into 'UNKNOWN' and run the program. What will happen?

  13. Example 3 – The Program INTEGER X, Y, Z OPEN (UNIT = 1, FILE = 'DATA1.TXT', STATUS = 'UNKNOWN') READ (1, *) X, Y PRINT*, X, Y, Z X = 50 Y = 60 Z = 70 WRITE (1, *) Z, Y, X CLOSE (1) END

  14. Loop READ • What if we do not know the number of values in a file? • READ (UNITNO, *, END = NUMBER) VARIABLE LIST • NUMBER is the line number of the statement where control will be transferred after all the data from the file is read

  15. Example 4 – Loop READ REAL NUM, SUM, AVG INTEGER COUNT OPEN (UNIT = 7, FILE = 'DATA1.TXT', STATUS = 'OLD') SUM = 0 COUNT = 0 • READ (7, *, END = 222) NUM SUM = SUM + NUM COUNT = COUNT + 1 GOTO 111 • AVG = SUM/COUNT PRINT*, AVG END

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