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Assembly and Fortran

B side: Fortran, the language that speaks maths

A cassette tape with a handwritten label: “B Side. Fortran, the language that speaks maths.”

Fortran lets you write maths in a form that a machine can run. The name comes from FORmula TRANslation. A program called the compiler translates your formulas into the machine tongue.

A long history, one language

Section titled “A long history, one language”

Fortran started in 1957. It is one of the oldest languages that people still use. It changed over time, as English changed from the time of Shakespeare to today.

Dialect Year What it added
FORTRAN 77 1978 The form of old programs: fixed columns, capital letters
Fortran 90 1991 Free-form text, arithmetic on full arrays, modules
Fortran 2008 2010 Coarrays for parallel work, DO CONCURRENT
Fortran 2018 and 2023 2018, 2023 More parallel features and more built-in procedures

We learn modern Fortran (2008 to 2023). The old FORTRAN 77 dialect does not have many of the words on this site.

The parts of speech on the B side

Section titled “The parts of speech on the B side”
  • Verbs are statements that do something. PRINT shows values. CALL runs a subroutine. ALLOCATE makes space for an array.
  • Nouns are types of value. INTEGER is a whole number. REAL is a number with a decimal point. CHARACTER is text.
  • Adjectives are attributes. They describe a noun. PARAMETER means “this value never changes”. ALLOCATABLE means “the program sets the size when it runs”.
  • Adverbs change a verb. CONCURRENT in DO CONCURRENT tells the compiler that the steps can happen in any order.
  • Idioms are built-in procedures: ready-made maths phrases. SQRT gives a square root. SUM adds a full list. MATMUL multiplies two tables of numbers.
  • Grammar marks are the maths signs: + - * / **. The = sign means “put the value on the right into the name on the left”.
  • Notes to the translator are structure words. PROGRAM, MODULE and CONTAINS give the compiler the structure of the text.

The shape of one sentence

Section titled “The shape of one sentence”

A line of Fortran looks like a line of maths:

energy = 0.5 * mass * speed**2   ! kinetic energy
Part In the example Meaning
Name energy The noun that gets the result
Assignment mark = Put the result into the name
Formula 0.5 * mass * speed**2 Maths, written almost as on paper
Comment ! kinetic energy A note for people. The compiler ignores it.

What the B side says well

Section titled “What the B side says well”
  • You write formulas as maths.
  • A full array is one noun. One line can do arithmetic on thousands of values.
  • The compiler finds many mistakes before the program runs.
  • The same text works on many different machines.

What the B side cannot say easily

Section titled “What the B side cannot say easily”
  • Fortran has no words for the screen, the keyboard chip or sound.
  • To control the hardware, Fortran needs help from C or from Assembly.

Fortran has no reserved words

Section titled “Fortran has no reserved words”

In most programming languages, a keyword cannot be a name. Fortran is different. It has no reserved words. You can name a variable real or if. This is legal, but it makes the text hard to read. Do not do it.

The segments

Section titled “The segments”

Each segment below has a B page. Open a segment to see its strengths and its words.