1. Introduction to FORTRAN
Shyh-Kang Jeng
Department of Electrical Engineering/
Graduate Institute of Communication Engineering
National Taiwan University

2. Reference
彭國倫, Fortran 95 程式設計, 碁峰, 2001.

3. Outline History of FORTRAN Basics Declaration Program Flow Control
Arrays
Functions
Pointers
Modules

4. History of FORTRAN FORmula TRANslator First FORTRAN compiler
John Backus, IBM, 1957
1st high level programming language
Most popular in 1960’s
FORTRAN 66
1st ANSI standard FORTRAN
FORTRAN 77, 1978
FORTRAN 90, 1992
Pointers and OO
FORTRAN 95, 1997
Support for parallel computation

5. Fixed Format (*.f, *.for) C FIXED FORMATDEMO program main
write(*,*) ‘Hello’
write(*,*)
1’Hello’
100 write(*,*) ‘Hello’
10 Stop
end

7. Free Format (*.f90) ! Free Format program main
write(*,*) “Hello” ! This is also a comment
write(*,*) &
“Hello”
wri&
&te(*,*) “Hello”
end

8. Basic Data Types and Arithmetic Operators
INTEGER
REAL
COMPLEX
CHARACTER
LOGICAL
Arithmetic operators
+, -, *, /, **, ()

9. Demo Program program example integer a real b real*8 c complex d
character(len=10) s
logical t
a = 2 + 2*4 – 3
b = /2.0
c = 0.1
write(*,*) a, “ “, b, “ “, c
d = (1.0, 2.0) ! d = i
write(*,*) d
s = “Hello”
write(*,*) s
t = .true.
write(*,*) t
stop
end

10. Read Data and Formatted Output
program readWriteDemo
integer a, b, c
real d
complex e
read(*,*) a, b, c
write(*,100) a + b + c
100 format(I4)
d = 12.3
write(*, “(1X, F5.2)”) d
e = (1, 2)
write(*, 200) e
200 format(1X, F4.1, F4.1)
end

11. implicit and parameter Statements
program demo
implicit none
integer :: i =
real pi
write(*,”(‘ =‘, I4)”) i
parameter (pi = )
write(*,”(F4.2)”) sin(pi/6)
end

12. DATA Statement program demo implicit none integer a real b complex c
character* (20) str
data a, b, c, str /1, 2.0, (1, 2), ‘FORTRAN 77’/
write(*,*) a, b, c, str
stop
end

13. type Statement (FORTRAN 90)
program typeDemo
implicit none
type::person
character(len=30) :: name
integer :: age
end type person
type(person) :: a;
write(*,*) “Name:”
read(*,*) a%name
write(*,*) “Age:”
read(*,*) a%age
write(*,100) a%name, a%age
100 format(/,”Name: “, A10/,”Age:”,I3)
stop
end

14. if Statement and Logical Operations (FORTRAN 77)
PROGRAM Demo
IMPLICIT NONE
REAL speed
LOGICAL hasBarrier
WRITE(*,*) “speed:”
READ(*,*) speed
hasBarrier = .false.
IF ( speed .GT OR. hasBarrier ) THEN
WRITE(*,*) “Slow down”
ELSE
WRITE(*,*) “Keep going”
END IF
STOP
END

15. if Statement and Logical Operations (FORTRAN 90)
program Demo
implicit none
integer rain, windSpeed
write(*,*) “Rain:”
read(*,*) rain
write(*,*) “Wind:”
read(*,*) windSpeed
if( rain >= 500 .or. windSpeed >= 10 ) then
write(*,*) “Take one day off”
else
write(*,*) “Go to office”
endif
stop
end

16. Multiple if-else if Statement
program demo
implicit none
integer score
character grade
write(*,*) “Score:”
read(*,*) score
if ( score > 100 ) then
grade = ‘?’
else if ( score >= 90 ) then
grade = ‘A’
else if ( score >= 80 ) then
grade = ‘B’
else
end if
write(*,”(‘Grade:’, A1)”) grade
stop
end

17. Nested if Statement program demo implicit none integer score
character grade
write(*,*) “Score:”
read(*,*) score
if ( score > 100 ) then
grade = ‘?’
else
if ( score >= 90 ) then
grade = ‘A’
grade = ‘B’
end if
write(*,”(‘Grade:’, A1)”) grade
stop
end

18. select case Statement program demo implicit none integer score
character grade
write(*,*) “Score:”
read(*,*) score
select case(score)
case(90:100)
grade = ‘A’
case default
grade = ‘B’
end select
write(*,”(‘Grade:’,A1)”) grade
stop
end

19. goto Statement program NOT_RECOMMENDED implicit none real height
real weight
write(*,*) “height:”
read(*,*) height
write(*,*) “weight:”
read(*,*) weight
if( weight > height – 100 ) goto 200
100 write(*,*) “Under control”
goto 300
200 write(*,*) “Too fat!”
300 stop
end

20. Arithmetic goto program NOT_RECOMMENDED implicit none real a, b real c
data a, b /2.0, 1.0/
c = a - b
if ( c ) 10, 20, 30
10 write(*,*) ‘a < b’
goto 40
20 write(*,*) ‘a = b’
30 write(*,*) ‘a > b’
40 Stop
end

21. do Statement (.f90) program demo implicit none integer counter
integer parameter :: lines = 10
do counter=1, lines, 1
write(*,*) “Happy New Year”, counter
end do
stop
end

22. do Statement (*.for) PROGRAM demo IMPLICIT NONE INTEGER limit
PARAMETER (limit=10)
INTEGER counter
INTEGER ans
DATA ans /0/
DO 100, counter = 2, limit, 2
ans = ans + counter
100 CONTINUE
WRITE(*,*) ans
STOP
END

23. do while Statement (*.f90)
program demo
implicit none
integer, parameter :: limit = 10
integer counter
integer :: ans = 0
counter = 2
do while ( counter <= limit )
ans = ans + counter
counter = counter + 2
end do
write(*,*) ans
stop
end

24. cycle Statement (*.f90) program elevator implicit none
integer :: dest = 9
integer floor
do floor = 1, dest
if ( floor == 4 ) cycle
write(*,*) floor
end do
stop
end

25. exit Statement (*.f90) program WeightGuess implicit none
real, parameter :: weight = 45.0
real, parameter :: error =
real :: guess
do while ( .true. )
write(*,*) “Weight:”
read(*,*) guess
if ( abs(guess – weight) < error ) exit
end do
write(*,*) “Correct!”
stop
end

26. One-Dimensional Array
program Demo
implicit none
integer, parameter :: students = 5
integer student( students )
integer i
do i = 1, students
write(*,”(‘Number ‘, I2)”) i
read(*,*) student(i)
end do
do while ( .true. )
write(*,*) “Query”
read(*,*) i
if( i <= 0 .or. i>students ) exit
write(*,*) student(i)
stop
end

27. Two-Dimensional Array (1/2)
program MatrixAddition
implicit none
integer, parameter :: row = 2
integer, parameter :: col = 2
integer matrixA(row, col)
integer matrixB(row, col)
integer matrixC(row, col)
integer r
integer c
write(*,*) “Matrix A”
do r = 1, row
do c = 1, col
write(*,”(‘A(‘,I1,’,’,I1,’)=‘)”) r, c
read(*,*) matrixA(r,c)
end do

28. Two-Dimensional Array (1/2)
write(*,*) “Matrix B”
do r = 1, row
do c = 1, col
write(*,”(‘B(‘,I1,’,’,I1,’)=‘)”) r, c
read(*,*) matrixB(r,c)
end do
write(*,*) “Matrix A + B = “
matrixC(r,c) = MatrixB(r,c) + MatrixA(r,c)
write(*,”(‘C(‘,I1,’,’,I1,’)=‘,I3)”) r, c, &
matrixC(r,c)
stop
end

29. Declaration of Arrays integer a(5) integer a(0:5) integer a(-3:3)
integer b(2:3, -1:3)

30. Setting Array Data integer a(5) data a /1, 2, 3, 4, 5/ integer i
data (a(i), i=2,4) /2, 3, 4/
integer a(2,2)
integer I, j
data ( (a(I,j), i=1,2), j=1,2) /1, 2, 3, 4/

31. Column Major Storage A(1,1) A(3,1) A(2,2) A(3,2) A(1,3) A(2,3) A(3,3)

32. Adjustable Array (*.f90) program Demo implicit none integer students
integer, allocatable :: a(
integer I
write(*,*) “How many students:”
read(*,*) students
allocate( a(students) )
do I = 1, students
write(*, “(‘Number ‘, I3)”) I
read(*,*) a(i)
end do
deallocate( a )
stop
end

33. Subroutines program example implicit none call message() stop end
subroutine message()
write(*,*) “Hello.”
return

34. Pass by Reference program example implicit none integer :: a = 1
integer :: b = 2
write(*,*) a, b
call add(a)
call add(b)
stop
end
subroutine add(num)
integer :: num
num = num + 1
return

35. Functions program example implicit none real :: a = 1 real :: b = 2
real, external :: add
write(*,*) add(a,b)
stop
end
function add(a, b)
real :: a, b
real :: add
add = a + b
return

36. common Statement program example implicit none integer :: a, b
common a, b
a = 1
b = 2
call showCommon()
stop
end
subroutine showCommon()
integer :: num1, num2
common num1, num2
write(*,*) num1, num2
return

37. Labeled common Blocks program example implicit none integer :: a, b
common /group1/ a
common /group2/ b
a = 1
b = 2
call showGroup1()
call showGroup2()
stop
end
subroutine showGroup1()
integer :: num
common /group1/ num1
write(*,*) num1
return

38. Block Data program example implicit none integer :: a, b common a, b
integer :: c, d
common /group1/ c, d
write(*,*) a, b, c, d
stop
end
block data
integer a, b
data a, b /1, 2/
integer c, d
common c, d
data c, d /3, 4/
end block data

39. Recursive Functions (*.f90)
program example
implicit none
integer n
integer, external :: fact
write(*,*) ‘N =‘
read(*,*) n
write(*,”(I2,’! = ‘,I8)” ) n, fact(n)
stop
end
recursive integer function fact(n) result(ans)
integer, intent(in) :: n
if( n <= 1 ) then
ans = 1
return
end if
ans = n * fact(n-1)

40. Pointers I program example implicit none integer, target :: a = 1
integer, pointer :: p
p=>a
write(*,*) p
a = 2
p = 3
write(*,*) a
stop
end

41. Pointers II program example implicit none integer, target :: a = 1
integer, pointer :: p
allocate(p)
p = 1
write(*,*) p
deallocate(p)
p=>a
stop
end

42. Pointers III program example implicit none integer, pointer : a(:)
allocate( a(5) )
a = (/ 1, 2, 3, 4, 5 /)
write(*,*) a
deallocate( a )
stop
end

43. Modules (1/4) module constant implicit none
real, parameter :: pi =
real, parameter :: g = 9.81
end module
module typedef
type player
real :: angle
real :: speed
real :: distance
end type

44. Modules (2/4) module shoot use constant use typedef implicit none
contains
real function AngleToRad( angle )
real angle
AngleToRad = angle * pi/180.0
return
end
subroutine GetDistance( person )
type(player) :: person
real rad, Vx, time

45. Modules (3/4) rad = AngleToRad( person%angle )
Vx = person%speed * cos( rad )
time = 2.0 * person%speed * sin( rad )/g
person % distance = Vx * time
return
end subroutine
end module

46. Modules (4/4) program example use shoot implicit none
integer, parameter :: players = 2
type(player) :: people(players) = (/ &
player(30.0, 25.0, 0.0 ), &
player(35.0, 21.0, 0.0 ) /)
integer :: i
do i = 1, players
call GetDistance( people(i) )
write(*,”(‘Player ‘,I1,’ =‘,F8.2)”) i, &
people(i)%distance
end do
stop
end