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[fortran/en] Fixed overly long comment lines (#5126)
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* [haskell/de] Added missing comment line about index operator

* [fortran/en] Fixed overly long comment lines

Including minor rewording and rearranging.  A comment was added at 'subroutine'
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@jklebes
jklebes authored Sep 25, 2024
1 parent 2b9e893 commit 495272c
Showing 1 changed file with 52 additions and 34 deletions.
86 changes: 52 additions & 34 deletions fortran.html.markdown
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Original file line number Diff line number Diff line change
Expand Up @@ -30,7 +30,8 @@ program example ! declare a program called example.
! All declarations must come before statements and expressions.
implicit none ! prevents dynamic declaration of variables (recommended!)
implicit none ! prevents dynamic declaration of variables
! Recommended!
! Implicit none must be redeclared in every function/program/module...
! IMPORTANT - Fortran is case insensitive.
Expand All @@ -45,10 +46,14 @@ program example ! declare a program called example.
complex :: w = (0, 1) ! sqrt(-1)
character(len=3) :: month ! string of 3 characters.
real :: array(6) ! declare an array of 6 reals.
real, dimension(4) :: arrayb ! another way to declare an array.
integer :: arrayc(-10:10) ! an array with a custom index.
real :: array2d(3, 2) ! multidimensional array.
! declare an array of 6 reals.
real :: array(6)
! another way to declare an array.
real, dimension(4) :: arrayb
! an array with a custom index -10 to 10 (inclusive)
integer :: arrayc(-10:10)
! A multidimensional array.
real :: array2d(3, 2)
! The '::' separators are not always necessary but are recommended.
Expand Down Expand Up @@ -76,8 +81,8 @@ program example ! declare a program called example.
! Assignment & Arithmetic
! =======================
Z = 1 ! assign to variable z declared above (case insensitive).
Z = 1 ! assign to variable z declared above
j = 10 + 2 - 3
a = 11.54/(2.3*3.1)
b = 2**3 ! exponentiation
Expand All @@ -86,7 +91,7 @@ program example ! declare a program called example.
! ===================================
! Single-line if statement
if (z == a) b = 4 ! condition always need surrounding parentheses.
if (z == a) b = 4 ! conditions always need parentheses.
if (z /= a) then ! z not equal to a
! Other symbolic comparisons are < > <= >= == /=
Expand All @@ -98,13 +103,13 @@ program example ! declare a program called example.
b = 5 ! execution block must be on a new line.
else
b = 10
end if ! end statement needs the 'if' (or can use 'endif').
end if ! end statement needs the 'if'
if (.NOT. (x < c .AND. v >= a .OR. z == z)) then ! boolean operators.
inner: if (.TRUE.) then ! can name if-construct.
b = 1
end if inner ! then must name endif statement.
end if
endif ! 'endif' is equivalent to 'end if'
i = 20
select case (i)
Expand All @@ -128,16 +133,16 @@ program example ! declare a program called example.
j = -1
end select monthly
do i = 2, 10, 2 ! loops from 2 to 10 (inclusive) in increments of 2.
do i = 2, 10, 2 ! loops from 2 to 10 (inclusive) in steps of 2.
innerloop: do j = 1, 3 ! loops can be named too.
exit ! quits the loop.
end do innerloop
cycle ! jump to next loop iteration.
end do
! Goto statement exists but it is heavily discouraged though.
! Goto statement exists but it is heavily discouraged.
goto 10
stop 1 ! stops code immediately (returning specified condition code).
stop 1 ! stops the program, returns condition code 1.
10 j = 201 ! this line is labeled as line 10
! Arrays
Expand Down Expand Up @@ -209,8 +214,12 @@ program example ! declare a program called example.
! we can have multiple format specifications.
print "(I5,F6.2,E6.2)", 120, 43.41, 43.41
print "(3I5)", 10, 20, 30 ! 3 repeats of integers (field width = 5).
print "(2(I5,F6.2))", 120, 43.42, 340, 65.3 ! repeated grouping of formats.
! 3 repeats of integers (field width = 5).
print "(3I5)", 10, 20, 30
! repeated grouping of formats.
print "(2(I5,F6.2))", 120, 43.42, 340, 65.3
! We can also read input from the terminal.
read (*, *) v
Expand All @@ -225,8 +234,9 @@ program example ! declare a program called example.
! To read a file.
open (newunit=m, file="records.txt", status="old")
! The file is referred to by a 'new unit number', an integer that the compiler
! picks for you.
! The file is referred to by a 'new unit number',
! an integer that the compiler picks for you.
read (unit=m, fmt="(3F10.2)") a, b, c
close (m)
Expand All @@ -241,7 +251,7 @@ program example ! declare a program called example.
call cpu_time(v) ! sets 'v' to a time in seconds.
k = ior(i, j) ! bitwise OR of 2 integers.
v = log10(x) ! log base 10.
i = floor(b) ! returns the closest integer less than or equal to x.
i = floor(b) ! converts b to integer by rounding down.
v = aimag(w) ! imaginary part of a complex number.
! Functions & Subroutines
Expand All @@ -252,7 +262,7 @@ program example ! declare a program called example.
call routine(a, c, v) ! subroutine call.
! A function takes a list of input parameters and returns a single value.
! A function takes several input parameters and returns a single value.
! However the input parameters may still be modified and side effects
! executed.
Expand All @@ -261,21 +271,22 @@ program example ! declare a program called example.
! Function calls can also be evoked within expressions.
print *, func2(3, 2, k)
! A pure function is a function that doesn't modify its input parameters
! or cause any side-effects.
! A pure function is a function that doesn't modify its input
! parameters or cause any side-effects.
m = func3(3, 2, k)
contains ! Zone for defining sub-programs internal to the program.
contains ! Start defining the program's internal procedures:
! Fortran has a couple of slightly different ways to define functions.
integer function func(a, b, c) ! a function returning an integer value.
! implicit none ! subvariable fields can no longer declare implicit none
integer, intent(in) :: a, b, c ! type of input parameters defined inside the function.
! implicit none ! - no longer used in subvariable fields
integer, intent(in) :: a, b, c ! type of input parameters
! the return variable defaults to the function name.
if (a >= 2) then
func = a + b + c ! the return variable defaults to the function name.
return ! can return the current value from the function at any time.
func = a + b + c
return ! returns the current value at 'func'
end if
func = a + c
Expand All @@ -286,24 +297,29 @@ contains ! Zone for defining sub-programs internal to the pro
integer, intent(in) :: a, b ! can declare and enforce that variables
!are not modified by the function.
integer, intent(inout) :: c
integer :: f ! function return type declared inside the function.
integer :: cnt = 0 ! GOTCHA - initialisation implies variable is
!saved between function calls.
integer :: f
! function return type declared inside the function.
integer :: cnt = 0 ! GOTCHA -
! assigning a value at initalization
! implies that the variable is
! saved between function calls.
f = a + b - c
c = 4 ! altering the value of an input variable.
c = 4 ! changing value of input variable c.
cnt = cnt + 1 ! count number of function calls.
end function func2
pure function func3(a, b, c) ! a pure function can have no side-effects.
pure function func3(a, b, c) ! a pure function has no side-effects.
integer, intent(in) :: a, b, c
integer :: func3
func3 = a*b*c
end function func3
! a subroutine does not return anything,
! but can change the value of arguments.
subroutine routine(d, e, f)
real, intent(inout) :: f
real, intent(in) :: d, e
Expand All @@ -312,7 +328,8 @@ contains ! Zone for defining sub-programs internal to the pro
end subroutine routine
end program example ! End of Program Definition -----------------------
end program example
! End of Program Definition -----------------------
! Functions and Subroutines declared externally to the program listing need
! to be declared to the program using an Interface declaration (even if they
Expand Down Expand Up @@ -350,7 +367,8 @@ module fruity
use fruit, only: apple, pear ! use apple and pear from fruit module.
implicit none ! comes after module imports.
private ! make things private to the module (default is public).
! By default all module data and functions will be public
private ! Instead set default to private
! Declare some variables/functions explicitly public.
public :: apple, mycar, create_mycar
! Declare some variables/functions private to the module (redundant here).
Expand Down

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