Input / Output

1
Chapter 5

• Input / Output

2
Control over input output

• The input and output are basically facilitates a
  communication between the user and the program.

External media
Computers memory
Keyboard Disk file Magnetic type etc.
Real Integer Character etc.
Input
Convert to internal form
Display Printer Disk file Magnetic type etc.
Output
Convert to external form
Input and output editing
3
Types of I/O Statements

• There are two basic types of I/O statements
• in Fortran 90
• 1) List-directed (Without Formatted)
• 2) Formatted (Programmer Formatted)

4
Formatted Output

• The simpler of two output statements in Fortran
  is
• print statement
• print format-specifier,
  output-list
• where format-specifier is one of the following
• 1) (an asterisk)
• 2) A character constant or a character variable
  (or expression or array) whose value specifies
  the format for the output.
• 3) The label of a format statement
• print statement displays the values of the items
  in the output-list on a new line.

5
Formatted Output

• The format-specifier specifies the format in
  which values of the expressions in the output
  list are to be displayed.
• In the second type of format-specifier, the
  formatting information is given as a character
  string that consists of format descriptors,
  separated by commas and enclosed in parentheses
• (list of format descriptors) or (list of
  format descriptors)
• In the third case, the formatting information is
  supplied by a format statement whose label is
  specified. This statement has the form
• label format (list of format
  descriptors)
• where label is an integer in the range 1 through
  99999.

6
Formatted Output

• For some Fortran compilers, the first character
  of each line of output directed to a printer is
  used to control the vertical spacing.
• black Normal spacing advance to the next line
  before printing
• 0 Double spacing skip one line before
  printing
• 1 Advance to top of next page before
  printing
• Overprint the last line printed
• There are many format descriptors that may be
  used in format specifiers. A list is presented in
  the following table.

7
Format Descriptors
8
Format Descriptors
9
Formatted Output

• Example
• print (I3) , N
• The format descriptor I3 specifies that the value
  to be printed is an integer and is to be printed
  in the first three positions of a line. If the
  value of N is 15, the three positions are filled
  with _15 (where _ denotes a blank).

10
Integer Output- The I descriptor

• Integer values that are output using an I
  descriptor are right-justified in fields of the
  specified sizes that is each value is displayed
  so that its last digit appears in the rightmost
  position of the field. For example, if the values
  of the integer variables
• Number, L, and Kappa are
• Integer Number 3, L 5378, Kappa -12345
• then the statements
• print (1X, 2I5, I7, I10) , Number, Number -3,
  L, Kappa
• print (1X, 2I5.5, I7, I10.7) , Number, Number
  -3, L, Kappa
• print (1X, 2I5.0, I7, I10) , Number, Number -3,
  L, Kappa
• or

11
Integer Output- The I descriptor

• Print 30, Number, Number -3, L, Kappa
• Print 31, Number, Number -3, L, Kappa
• Print 32, Number, Number -3, L, Kappa
• 30 format (1X, 2I5, I7, I10)
• 31 format (1X, 2I5.2, I7, I10.7)
• 32 format (1X, 2I5.0, I7, I10)
• produce the following output
• _ _ _ _ _ 3 _ _ _ _ 0 _ _ _ 5378 _ _ _ _ -12345
• _ _ _ _ 0 3 _ _ _ 0 0 _ _ _ 5378 _ _ - 0 012345
• _ _ _ _ _ 3 _ _ _ _ _ _ _ _ 5378 _ _ _ _ -12345

12
Real Output- The F, E, ES and EN Descriptors

• Integer and real outputs are right-justified in
  their fields. In a Fw.d descriptor, w specifies
  the total width of the field in which to display
  a real value, and d is the number of digits to
  the right of the decimal point.
• Example
• integer In 625, Out -19
• real A 7.5, B 0.182, C 625.327
• using the statement
• print (1X, 2I4, 2F6.3, F8,3), In, Out, A, B, C
• The resulting output is
• _ _ 6 2 5 _ - 1 9 _ 7 . 5 0 0 _ 0 . 1 8 2 _ 6 2
  5 . 3 2 7

13
Real Output- The F, E, ES and EN Descriptors

• For a descriptor Fw.d, one should have w gt
  d3 to allow for the sign of the number, the
  first digit, and the decimal point (-,0.).
• Lets see the E descriptor with an example
• The values of real variables A, B, C and D
  are given by
• real A0.12345E8, B0.0237, C4.6E-12,
  D-76.1684E12
• the statement
• print (1X, 2E15.5, E15.4, E14.4), A, B, C,
  D
• produces output like the following
• _ _ _ _ _0.12345E08_ _ _ _0.23700E-01_ _ _ _
  _0.4600E-11_ _ _-0.7617E14
• As with the F descriptor, a field is
  asterisk-filled if it is not large enough for the
  value.

14
Real Output- The F, E, ES and EN Descriptors

• The scientific descriptor ES is used in the same
  manner as the E descriptor. Only difference is
  that the values are normalized.
• The engineering descriptor EN also is used in the
  same manner as the E descriptor. Only difference
  is that exponent is constrained to be a multiple
  of 3.

15
Character Output

• Character data may also be displayed by using an
  A format descriptor of the form rA or rAw. In the
  first form, the field width is determined by the
  length of the character value being displayed.
• In the second form, if the field width exceeds
  the length of the character value, that value is
  right-justified in the field.

16
Positional descriptors - X and T

• A descriptor of the form nX can be used to insert
  n blanks in an output line. A tab descriptor of
  the form Tc causes the next output field to begin
  at the specified position c on the current line.
• For example
• print 75, John Q. Doe, CPSC, Number
• 75 format (1X, A11, 3X, A4, 2X, I3)
• or
• 75 format (1X, A11, T16, A4, 2X, I3)
• will produce the output
• _ John_Q._Doe_ _ _CPSC_ _141

17
Repeating Groups and The Slash (/) Descriptor

• It is possible to repeat some format descriptors
  by preceding them with a repetition indicator.
• For example ? 3F10.2 is equivalent to F10.2,
  F10.2, F10.2.
• A single output statement can be used to display
  values on more than one line, with different
  formats, by using a slash (/) descriptor.
• Consider the following statement
• print (fmt88) Values, N, A, M, B, C, D
• 88 format (1X, A, 3/ 1X, 2(I10, F10.2) // 1X,
  2E15.7)

18
Formatted Input

• read statement has two forms the simpler form
  is,
• read format-specifier, input-list
• For example read 5, I, J, K
• INTEGER INPUT
• Integer data can be read using the I descriptor
  of the form rIw, where w indicates the width of
  the field.
• For example
• integer I, J, K
• read (I6, I4, I7), I, J,
  K
• or
• read 5, I, J, K
• 5 format (I6, I4, I7)

19
Formatted Input

• REAL INPUT
• We can enter a real number in 2 ways
• 1) Enter the numbers without decimal points.
• For example enter the following values for real
  variables A, B, C, D and E.
• A6.25, B-1.9, C75.0, D.182,
  E625.327
• read (F3.2, 2F3.1, F3.3, F6.3),
  A, B, C, D, E
• enter the data in the form
  625-19750182625327
• 2) Enter the decimal point as part of the input
  value
• read (4F5.0, F8.0), A, B, C, D, E
• enter the data in the following form
• _6.25_-1.9_ _75._.182_625.327

20
Formatted Input

• CHARACTER INPUT
• When a read statement whose input list contains a
  character variable is executed, all characters in
  the field associated with the corresponding A
  descriptor are read.
• For example Assume the line of data is
• Fourscore_and_seven_years_ago
• and read by statements
• character(6) Speech1,Speech2
• read (2A) , Speech1, Speech2
• the values assigned to Speech1 and Speech2 are
• Speech1 Foursc
• Speech2 ore_an

21
Reading Exercises

• ELLIS BOOK
• Do example 3.2 and self-test exercise 3.2 on
  pages 60 and 63.
• Read pages between 56 and 60.

22
Write Statement

• The write statement has the following form
• write (control-list)
  output-list
• where control-list may include items selected
  from the following
• 1) A unit specifier, which is a integer
  expression whose value designates the output
  device
• unit unit-specifier or simply
  unit-specifier
• 2) A format specifier that may be any of the
  forms allowed in the print statement.
• fmt format-specifier or simply
  format-specifier
• 3) An ADVANCEclause of the form
• advance character-expression
• where the value of character-expression is either
  no or yes.
• 4) Any other items that are especially useful in
  file processing.

23
Read Statement

• The read statement has the following form
• read (control-list) input-list
• where control-list may include items selected
  from the following
• 1) A unit specifier, which is a integer
  expression whose value designates the input
  device
• unit unit-specifier or simply
  unit-specifier
• 2) A format specifier that may be any of the
  forms allowed in the print statement.
• fmt format-specifier or simply
  format-specifier
• 3) An ADVANCEclause of the form
• advance character-expression
• where the value of character-expression is either
  no or yes.
• 4) An iostatclause to detect an input error or
  end-of-file condition.

24
Reading Exercise

• ELLIS BOOK
• Read pages between 230 and 258.
• Study self-test exercises 9.2 and summary.

25
File Processing

• Storing/reading large data sets in/from a file
  are more convenient for data processing.
• OPENING FILES
• In order to open a file in Fortran a unit number
  must be connected to it and several items of
  information about the file must be supplied.
• Open statement is the following form
• open (open_specifier_list)
• where open-list includes
• 1) unit indicating a unit number.
• 2) file (character-expression ) indicating the
  name of the file.
• 3) status (character-expression ) where the
  value of character-expression is one of

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File Processing (Opening files)

• old
• new
• replace
• (or unknown). And scratch
• 4) action allowed_actions
• where allowed_actions are a character expression
  whose value is one of
• read
• write
• readwrite (default) (statusscratch)
• 5) positioncharacter-expression where the
  value of character-expression is one of
• rewind (The file at its initial point)
• append (The file at its end)

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File Processing (Opening files)

• asis (Leave its position unchanged)
• 6) IOSTATstatus-variable where
  status-variable is an integer variable to which
  the value zero is assigned if the file is opened
  successfully and a positive value is assigned
  otherwise.
• NOTE If file name is not presented then
  statusscratch must be specified
• EXAMPLE
• open (unit 12, File INFO.DAT, status
  old, action read, position rewind,
  iostat OpenStatus)
• where OpenStatus is an integer variable.
• Sometimes it is convenient to declare a character
  variable to store the name of file in a way that
  the user input the name.

28
File Processing (Opening files)

• EXAMPLE
• Character (12) FileName
• write (unit, (1X, A), advance no) Enter
  the name of data file
• read (unit, fmt) FileName
• and then use the following open statement
• open (unit 12, file FileName, status old,
  action read,
• position
  rewind, iostat OpenStatus)
• if the file is successfully opened, the status
  variable OpenStatus will be set to 0.
• If (OpenStatus gt 0) stop cannot open file
  

29
File Processing (Closing files)

• The close statement has a function opposite that
  of the open statement and it is used to
  disconnect a file from its unit number.
• Close (close-specifier-li
  st)
• where close-specifier-list must include a unit
  specifier and may include other items such as
  iostat and status. status may take character
  expressions such as keep or delete.
• FILE INPUT/OUTPUT
• Once a file has been disconnected to a unit
  number, data can be read from or written to that
  file using the general forms of the read and
  write statements. During this process iostat can
  be positive negative or zero.
• 1) A positive value in case of an input error
  occurs
• 2) A negative value if the end of data is
  encountered but no input error occurs

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File Processing (File Input/Output)

• 3) Zero value if neither an input error nor the
  end of data occurs.
• Example
• do
• read (12, fmt, iostat InputStatus) Code,
  Temperature, Pressure
• ! If end of data, terminate repetition
• if (InputStatus lt 0) exit
• ! If input error, stop execution
• if (InputStatus gt0) stop Input error
• ! Otherwise continue processing data
• Count Count 1
• .
• .
• SumOfPressuresPressure
• end do

31
File Processing (rewind/backspace)

• Sometimes it is necessary to reposition a file so
  that data values that have already been read can
  be read again.
• To reposition a file at its beginning use a
  rewind statement
• rewind (auxlist)
• To reposition a file at the beginning of the
  proceeding line use backspace statement
• backspace (auxlist)
• auxlist consist of a unit specifier and,
  optionally, an iostat specifier.

32
End of File

• To permit detection of the end-of-file mark, an
  exeption specifier of the form iostatInteger
  variable may be included in the Control list of
  the read statement
• read (unit , fmt , iostat
  Integer_variable) Input list
• The designated Integer variable will be zero
  after a normal read operation it will have a
  negative value if an end-of-file mark is read.
• Example
• integer E_O_F
• do
• read (unit, fmt, iostatE_O_F) Next_Datum
  ! Set E_O_F
• if (E_O_F lt 0) exit
  ! Test E_O_F
• .
• .
• .
• enddo

33
Exercises on I/O operations

• ELLIS BOOK
• Read pages between 230-260.
• Do self exercises 9.1 and 9.2 on pages 248 and
  254.
• Exercises on File processing
• Read pages between 264-288.