a side-by-side reference sheet

grammar and invocation | variables and expressions | arithmetic and logic | strings | dates and time | arrays | arithmetic sequences | functions | execution control | file handles | processes and environment

vectors | matrices

Grammar and Invocation

file suffixes

The suffixes used for source files, header files, and compiled object files.

fortran:

The gfortran compiler will treat files with .f and .f77 suffixes as the older fixed format source code, and it will treat files with .f90 and .f95 suffixes as free format source code conforming to the 1990 and 1995 Fortran standards.

Traditionally Fortran does not have header files. The Fortran 90 standard introduced modules. To support the feature the compiler will generate .mod files whenever a source file with a module definition is encountered. They contain type declarations like C headers, but unlike C headers they are not intended to be edited by people.

block delimiters

fortran:

The list of keywords is not exhaustive.

Variables and Expressions

undeclared variable type

fortran:

This makes undeclared variables starting with 'q' integers:

implicit integer q

undefined variable access

fortran:

It is possible to require that all variables are declared:

implicit none

Variable which are declared but not initialized are assigned zero values.

Arithmetic and Logic

boolean type

The boolean type.

true and false

The literals for true and false.

falsehoods

Values which are false in a boolean context.

logical operators

The logical operators for conjunction, disjunction, and negation.

fortran:

.eqv. .neqv.

apl:

APL also has operators for "nand" and "nor":

⍲ ⍱

relational operators

min and max

integer type

integer literal

The syntax for integer literals.

apl:

The minus sign can be used as a unary operator, but applies to the entire array. The following expressions are the same:

- 4 5 6
¯4 ¯5 ¯6

unsigned integer type

Strings

sprintf

fortran:

Fortran format strings use these expressions:

width and precision are integers. width is the field width in characters. Other characters in the format string are ignored.

Dates and Time

current local date and time

sleep

cpu usage

Arrays

Arithmetic Sequences

unit difference

difference of 10

difference of 0.1

Functions

Execution Control

break/continue

fortran:

Fortran has a continue statement which is a no-op statement used as a target for goto statements.

Here is an example of using exit to terminate what would otherwise be an infinite loop:

n = 1
do
   if (n > 10) exit
   write(*, *) n
   n = n + 1
end do

Labels can be provided for nested do loops. The labels can be provided as arguments to exit and cycle:

  foo: do
     bar: do n = 1, 10, 1
        write(*,*) n
        exit foo
     end do bar
  end do foo

File Handles

standard file handles

The file handles for standard input, standard output, and standard error.

fortran:

Fortran uses integers which it calls unit identifiers for file descriptors. The unit descriptors 5, 6, and 0 are often but not always used for stdin, stdout, and stderr.

Unit descriptors are provided as the first argument to read and write. If the first argument of read is an asterisk, it will use stdin. If the first argument of write is an asterisk, it will use stdout.

write formatted string to stdout

How to print a formatted string to standard out.

fortran:

Notation used in Fortran format strings.

Processes and Environment

Vectors

Matrices

Fortran

The GNU Fortran Compiler
Fortran 77 Tutorial
Fortran 90 Tutorial
Fortran Standards Documents
BLAS: A Quick Reference Guide (pdf)

Modern Fortran compilers support two source code formats: the traditional fixed format and the free format introduced with Fortran 90.

If a Fortran source file has a .f suffix, the gfortran compiler expects the code to have fixed format. If the suffix is .f90 or .f95 it expects free format code.

Here is an example of fixed format code:

C Hello World
* in Fortran 77

      program hello
10000 write(*,*) 'Hello,'
     + , ' World!'
      end program hello

This first column can contain a 'C', 'c', or '*' to indicate the line is a comment.

Columns 1 through 5 can contain an optional statement label. A statement label consists of digits. The statement label may contain leading zeros which are ignored. A statement label cannot consist entirely of zeros.

If column 6 contains a non-space character and columns 1 through 5 are blank, then the line is treated as a continuation of the previous line. The continuation character is not itself part of the statement, so any non-space character can be used, but '+' is a common choice.

Columns 7 through 72 contain the statement.

Columns 73 through 80 can contain optional sequence numbers. They were formerly used to help keep punch cards in the correct order.

Here is an example of free format code:

! Hello World in Fortran 90

program hello
  write(*,*) 'Hello,' &
       , ' World!'
end program hello

There are no special columns in free format code. There is no limit on the length of lines or statements. If it is desirable to split a statement up over multiple lines, the '&' character can be used to indicate the statement continues on the following line.

APL

A Dictionary of APL
A Programming Language

The first issue one must resolve when getting started with APL is figuring out how to enter the special characters.

One technique is to add a input method to your desktop environment. Here are APL input methods for Mac OS X and Windows. The Windows input method uses AutoHotkey. If you don't have AutoHotkey installed, you can use the .exe file that was generated using AutoHotkey. Otherwise you can use the .ahk file.

The notation in the above input methods is derived from the standard names and synonyms for the symbols in the APL community. The standard name for ⍋ is "grade". The above input methods use an ampersand prefix in front of the standard name. Thus, to create a ⍋ character, one types "@grade" when the input method is in effect.