Add a folder for Fortran

Fortran/HelloWorld.f90

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+                           !                       | Like ... in XML
+program hello              ! Start the program     | <program hello>
+  print *, "Hello, World!" ! Print "Hello, World!" |   <print>Hello, World</print>
+end program hello          ! End the program       | </program>

Fortran/IO.f90

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+program io_example
+  CHARACTER*10 :: input
+  CHARACTER*20 :: file_input
+  !
+  ! Output
+  !
+
+  ! The print command is used to print text on screen.
+  print *, "Hello, World!"
+  ! write(*,*) is equivilent
+  write (*,*) "Hello, World!"
+
+  ! File IO
+  ! Open a file descriptor 20 for my.txt
+  ! NOTE: usually you would have a constant for it, but you don't have to.
+  open (unit=20, file="my.txt", action="write", status="replace")
+  ! Write to it
+  write (20,*) "Hello, my.txt!"
+  ! Close it
+  close (20)
+  ! (that was basically a fopen(3), fwrite(3) and fclose(3))
+
+  !
+  ! Input
+  !
+
+  ! Get input from standard input
+  read (*, *) input
+  ! Spit it out to standard output
+  print *, input
+
+  ! File IO
+  ! Open a file descriptor 12 for my.txt
+  open (unit=12, file="my.txt", action="read", status="old")
+  ! Read it
+  ! (the '(A)' makes it read the whole line)
+  read (12,'(A)') file_input
+  ! Spit it out to stdout
+  print *, file_input
+  ! Close it
+  close (12)
+  ! (aka fopen(3), fread(3) and fclose(3))
+end program io_example

Fortran/Logic.f90

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+program logic_example
+  ! Variables
+  LOGICAL :: myVar
+  ! Integer(16)
+  INTEGER (16) :: myInt = 4, myNewInt
+
+  !
+  ! if statement
+  !
+  myVar = .TRUE.
+
+  if (myVar) then
+     print *, "It works!"
+  end if
+
+  !
+  ! Comparison Operators
+  !
+  if (myInt .GT. 1) then ! or if (myInt > 1) then...
+     print *, "It works!"
+  end if
+
+  if (myInt .LT. 5) then ! or if (myInt < 5) then...
+     print *, "It works!"
+  end if
+
+  if (myInt .GE. 4 .AND. myInt .LE. 4) then ! or if (myInt >= 4 .AND. myInt <= 4) then...
+     print *, "It works!"
+  end if
+
+  if (myInt .EQ. 4 .AND. myInt .NE. 3) then ! or if (myInt == 4 .AND. myInt /= 3) then...
+     print *, "It works!"
+  end if
+
+  !
+  ! select case () [switch]
+  !
+  select case (myInt)
+  case (1)
+     print *, "Nope!"
+  case (2)
+     print *, "Nope!"
+  case (3)
+     print *, "Nope!"
+  case (4)
+     print *, "We have a winner!"
+  case default
+     print *, "Nooope!"
+  end select
+
+  !
+  ! do loop [for-like]
+  !
+  do myInt=0, 20
+     print *, myInt ** 2
+  end do
+
+  ! Can be nested
+  do myInt=1, 20
+     ! Third argument means count by twos
+     do myNewInt=1, 10, 2
+        print *, myInt ** myNewInt
+     end do
+  end do
+end program logic_example

Fortran/Math.f90

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+program math_example
+  ! Variables
+  INTEGER :: a, s, d, m
+  REAL :: dd
+  DOUBLE PRECISION :: dpd
+
+  a = 1 + 1 ! Set a to 1+1
+  s = 2 - 1 ! Set s to 2-1
+  d = 2 / 3 ! Set d to 2/3 or 0 (round down)
+  dd= 2.0 / 3.0 ! Set dd to 2/3 or 0.666666687
+  dpd=2.0 / 3.0 ! Set dpd to 2/3 or 0.66666668653488159
+  m = 2 * 2 ! Set m to 2*2
+
+  print *,a
+  print *,s
+  print *,d
+  print *,dd
+  print *,dpd
+  print *,m
+end program math_example

Fortran/README.md

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+# Fortran
+> Fortran is a programming language mainly used by the scientific community. Its name is a contraction of FORmula TRANslation, and its aim is to provide a way to tell computers to calculate complicated mathematical expressions, with more ease than assembly language.  
+>
+> ~[WikiBooks](https://wikibooks.org/wiki/Fortran)
+>
+Fortran is a language originally made in 1957, and since updated in 1958, 1962, 1966, 1977, 1991, 2003 and finally 2008. It was one of the first programming languages for an IBM computer.
+
+
+> ### Note
+> I'm going to be using Fortran 90, from 1991.
+>
+> Also, Fortran is case-insensitive, but I will be using lowercase.
+

Fortran/Variables.f90

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+program variable_example
+  !
+  ! Integers, strings and booleans
+  !
+  INTEGER :: myNumber = 0 ! Declare an integer, with value 0
+  INTEGER (16) :: myBigNumber ! Declare a 8-byte (64-bit) integer
+  INTEGER (1) :: myTinyNumber = 9 ! Fix a compile error
+  LOGICAL :: myBoolean = .TRUE. ! Declare a boolean
+  CHARACTER*3 :: myWord = "Pig" ! Declare a word myWord to Pig
+  ! Note that all variables by default are
+  ! mutable. For constant, try ,PARAMETER
+  LOGICAL, PARAMETER :: myConstantBoolean = .FALSE. ! A constant boolean.
+
+  REAL :: myFloat = 3.1415 ! Declare a REAL, aka a float
+  DOUBLE PRECISION :: myDouble = 3.141526 ! Declare a DOUBLE PRECISION, aka a double
+
+  !
+  ! Reassignment
+  !
+  myInteger = 1       ! Change myInteger from 0 to 1
+  myBigNumber = 11**myTinyNumber ! Set myBigNumber to 11^9 (overflows to negative)
+  myBoolean = .FALSE. ! Change myBoolean from .TRUE. to .FALSE.
+  myWord = "Dog"
+
+  !myConstantBoolean = .TRUE. ! This will not compile, as myConstantBoolean is constant!
+
+  myWord = "Food!" ! This does compile, but myWord only keeps Foo
+
+  ! Output the values
+  print *, myNumber !         => 0
+  print *, myBigNumber !      => 
+  print *, myBoolean !        => F
+  print *, myWord !           => Foo
+  print *, myConstantBoolean !=> F
+  print *, myFloat !          => 3.14150000
+  print *, myDouble !         => 3.1415259838104248
+end program variable_example