Input and output

Input streams

there are two ways of handling I/o list-directed

– done using default settings– PRINT*, num– READ*, num

formatted– controlled by the programmer– you can specify every detail of what is printed

Output statements

PRINT– only used for output to the screen

WRITE– used for output to files

PRINT statements

List directed– PRINT*, num

Formatted– PRINT ‘(1x, i5, f8.2)’, number, temperature

With format labels– PRINT 10, number, temperature– 10 FORMAT (1x, i5, f8.2)

Format descriptors

(1x, i5, f8.2)– 1 space, followed by a 5-digit integer,

followed by a real number taking up 8 spaces total with two after the decimal point.

A format descriptor designated the exact number of characters that will be printed and where they will be printed.

The integer format descriptor

i used for integers, can be repeated (5i) and can have width specified (i5)– INTEGER :: num– num = 123– PRINT ‘(i3)’, num -------------> 123– PRINT ‘(3i)’, num -------------> 123123123– PRINT *, num -------------> 123– PRINT ‘(i2)’, num -------------> **

The real number descriptor

F for ‘floating point’ (real) numbers. – Followed by an integer total field width, ‘.’,

then an integer number of decimal digits.– REAL :: num– num = 123.45– PRINT ‘(f8.2)’, num ---------------> 123.45– PRINT ‘(f6.2)’ , num --------------->123.45– PRINT*, num ---------------> 123.4500– PRINT ‘(f3.2)’, num ---------------> ***

The character data descriptor

a used for ‘alpha-numeric data’– CHARACTER(10) :: name– name = “Washington”– PRINT ‘(a10)’, name ---------------> Washington– PRINT ‘(a15)’, name ---------------> Washington_____– PRINT*, name ---------------> Washington– PRINT ‘(a5)’ ---------------> Washi

The spacing descriptors

X - stands for ‘print a blank space’ T - stands for ‘print a tab’

– INTEGER :: num1, num2– num1 = 123– num2 = 456– PRINT ‘(1x,i5,5x,i3)’, num1, num2 – ___123_____456– PRINT ‘(t5, i3), num1 ---------------> _____123

Difference between x and t

5x gives five spaces t5 tabs out to column 5 (gives only 4

spaces!) When used in tables together they are

easy to confuse.

Repetition and width

nX if first, specifies line spacing

nX n blanks or spaces printed

A number of characters matches list item

Aw w characters are printed

Iw integer is right-justified in w columns

Fw.d real no. is in w columns, d is decimal places

Carriage controls

FIRST EDIT DESCRIPTOR– ‘ ‘ OR 1X PRINTS A SPACE– ‘0’ DOUBLE LINE SPACING– ‘1’ PRINTS ON TOP OF PAGE– ‘+’ PRINTS WITHOUT SPACING

(OVERPRINTS)

SOME COMPILERS DON’T RECOGNIZE ALL OF THE ABOVE

Repeating Edit Descriptors

Place a number in front of descriptor

nI4 repeats I4 n times

3F5.2 repeats F5.2 3 times

4(5X,I2) repeats 5X & I2 4 times

More descriptors

Tw tabs over to column w

/ starts rest of statement on a new line

n(/) starts rest of statement in n lines

Ew.d reads numbers in scientific

notation

Literals

Individual characters may also be inserted in formats.– PRINT ‘(“$”, f6.2)’, price ----------> $123.45– PRINT ‘(10(“-”))’ ---------------> ==========

Printing tables First print the heading Then a loop fills in the body of the table

– PRINT ‘(t10, “Number”, t20, “Square”)’– DO n=1, 5– PRINT ‘(9x, i6, t20, i6)’, n, n**2– ENDDO

– ---------Number----Square– --------- 1---- 1– --------- 2---- 4– --------- 3---- 9– --------- 4---- 16– --------- 5---- 25

READ statements

List directed– READ*, num

Formatted– READ ‘(1x, i5, f8.2)’, number, temperature

With format labels– READ 10, number, temperature– 10 FORMAT (1x, i5, f8.2)

Reading real numbers

Data may come in in one of two ways– Numbers without decimal points

• the decimal digits are always filled

– Numbers with decimal points – REAL :: num– READ ‘(f6.2)’, num

– The data entered may be either with decimal point (123.45) or not ( 12345)

The WRITE statement

is used to write to files Underlies the PRINT statement PRINT*, is really WRITE (*,*) or WRITE (6,*) By default, write will send output to the default

output device.– This device is the monitor– It is identified by a number (UNIT = 6)– Often called ‘standard output’

WRITE default examples

WRITE (*, *) num1, num2 WRITE (*, ‘(i4,1x,i6)’) num1, num2 WRITE (*, 20) num1, num2 20 FORMAT (1x. I4, t12, i5) WRITE (UNIT = 6, FMT = 30) num1, num2

READ default settings

is used to read from files By default, read will read from the default

input device– This device is the keyboard– It is identified by the number (UNIT = 5)– Often called ‘standard input’

Default devices

UNIT 6 is standard output UNIT 5 is standard input It is an error to try to read from standard

output or write to standard input.

File processing

Data commonly comes to us in files. We will learn how to handle

– text files (ASCII characters)– rectangular, “flat files”– sequential access

Later the book will discuss– binary files– direct (random) access

Opening a file

To open a file use the OPEN statement.– First specify the UNIT number of the file– Then the name of the FILE– Other specifiers are

• STATUS (NEW, OLD, REPLACE)• ACTION (READ, WRITE, READWRITE)• POSITION (REWIND, APPEND, ASIS)• IOSTAT (0 = ok, >0 = error)

Examples

OPEN (UNIT=12, FILE=“mydata.dat”, STATUS = “OLD”, ACTION=“READ”, POSITION=“REWIND”, IOSTAT=OpenStatus)

OPEN(12,FILE=“mydat”) Both forms yield the same results due to

default settings

Using IOSTAT

IOSTAT means Input/Output Status If the value is placed in a variable it may be

used later in the program. OPEN (12,FILE=“mydata.dat”,

IOSTAT=OpenStatus) IF (OpenStatus > 0) STOP “**** Cannot open

file ****”

CLOSE

Any file that is OPENed should also be closed after your program is done using it.

CLOSE (12) Only the UNIT number needs to be specified.

READ, IOSTAT and END=

IOSTAT is used with READ to help a program stop reading from a file when it encounters the end of that file (eof).

READ (12, *, IOSTAT = InputStatus) num1, num2 IF (InputStatus < 0) EXIT Another method is READ (12,*, END=20) num1,

num2 20 PRINT*, “The end of the file has been

encountered”