FORTRAN 90
Lecture : Rafel Hekmat Hameed
University of Babylon
Subject : Fortran 90
College of Engineering
Year : Second B.Sc
Mechanical Engineering Dep.
Directed Input: The READ Statement
The READ statement can read input values into a set of variables from the
keyboard.
The READ statement has the following forms:
READ(*,*) var1, var2, ..., varn
Read*, var1, var2, ..., varn

The following example reads in four values into variables Factor, N,
Multiple and tolerance in this order.
INTEGER :: Factor, N
REAL :: Multiple, tolerance
READ(*,*) Factor, N, Multiple, tolerance

The following example reads in a string into Title, followed by three real
numbers into Height, Length and Area.
CHARACTER(LEN=10) :: Title
REAL :: Height, Length, Area
READ(*,*) Title, Height, Length, Area
Preparing Input Data:
The input data values must be separated by space or commas. For the
following READ
CHARACTER(LEN=5) :: Name
REAL
:: height, length
ϭ
INTEGER
:: count, MaxLength
READ(*,*) Name, height, count, length, MaxLength
The input data may look like the following:
"Smith" 100.0 25 123.579 10000
The execution of a READ always starts searching for input values with a new
input line.
INTEGER :: I, J, K, L, M, N
READ(*,*) I, J
READ(*,*) K, L, M
READ(*,*) N
If the above READ statements are used to read the following input lines,
100 200
300 400 500
600
Then I, J, K, L, M and N will receive 100, 200, 300, 400, 500 and 600,
respectively.
 If the input value is an integer and the corresponding variable is of REAL
type, the input integer will be convert to a real number. But, if the input
value is a real number and the corresponding variable is of INTEGER
type, an error will occur.
 Finally, a READ without a list of variables simply skips a line of input.
Consider the following:
INTEGER :: P, Q, R, S
READ(*,*) P, Q
READ(*,*)
READ(*,*) R, S
If the input lines are
100 200 300
400 500 600
Ϯ
700 800 900
The first READ reads 100 and 200 into P and Q and 300 is lost. The
second READ starts with a new input line, which is the second one. It does not
read in anything. The third READ starts with the third line and reads 700 and
800 into R and S. The third value on the third line, 900, is also lost.
Directed Output: The WRITE Statement
The WRITE statement can display the results of a set of expressions and
character strings. In general, WRITE displays the output on the screen. The
WRITE statement has the following forms:
WRITE(*,*) exp1, exp2, ..., expn
PRINT*, exp1, exp2, ..., expn
The first form starts with WRITE(*,*), followed by a list of arithmetic
expressions or character strings, separated by commas.

The following example displays the values of four variables on screen:
INTEGER :: Factor, N
REAL :: Multiple, tolerance
WRITE(*,*) Factor, N, Multiple, tolerance

The following example displays the string content of Title, followed by
the result of (Height + Length) * Area.
CHARACTER(LEN=10) :: Title
REAL :: Height, Length, Area
WRITE(*,*) Title, (Height + Length) * Area
ϯ
PROGRAM output
implicit none
character (len=15) :: name
integer :: iyear , imonths , iage
write(*,*) 'hello, what is your name'
read(*,*) name
write(*,*) "how old are you, (years and months)?"
read(*,*) iyears, imonths
iage=iyeats*12+imonth
write(*,*) name,'is',iage,'months old!'
stop
end
File I/O
It is also possible to read or write from files which are stored on some
external storage device, typically a disk (hard disk, floppy) or a tape. In Fortran
each file is associated with a unit number, an integer between 1 and 99.
Before you can use a file you have to open it.
OPEN ( unit= 1,file='aa.dat')
If you read data from file aa.dat, then read statement will be
Read (1,*) a,b,c
Or if you need to print your results in to output file bb.dat then the write
statement will be
OPEN ( unit= 22,file='bb.dat')
Write (22,*) x
ϰ
Examples (H.W)
Given three real numbers, its arithmetic mean (average), geometric mean
and harmonic mean are defined as follows:
Write a program to compute and display the means of three REAL variables
initialized with positive real values. Print your results in out put
ut file
Program Output
Data items: 1., 2., 3.
Arithmetic mean = 2.
Geometric mean = 1.81712067
Harmonic Mean = 1.63636363
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