Fortran

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Fortran_table_infobox_0

FortranFortran_table_caption_0
ParadigmFortran_header_cell_0_0_0 multi-paradigm: structured, imperative (procedural, object-oriented), generic, arrayFortran_cell_0_0_1
Designed byFortran_header_cell_0_1_0 John BackusFortran_cell_0_1_1
DeveloperFortran_header_cell_0_2_0 John Backus and IBMFortran_cell_0_2_1
First appearedFortran_header_cell_0_3_0 1957; 63 years ago (1957)Fortran_cell_0_3_1
Stable releaseFortran_header_cell_0_4_0 Fortran 2018 (ISO/IEC 1539-1:2018)
  / November 28, 2018; 2 years ago (2018-11-28)Fortran_cell_0_4_1
Typing disciplineFortran_header_cell_0_5_0 strong, static, manifestFortran_cell_0_5_1
Fortran_header_cell_0_6_0 .f, .for, .f90Fortran_cell_0_6_1
WebsiteFortran_header_cell_0_7_0 Fortran_cell_0_7_1
Major implementationsFortran_header_cell_0_8_0
Influenced byFortran_header_cell_0_9_0
InfluencedFortran_header_cell_0_10_0

Fortran (/ˈfɔːrtræn/; formerly FORTRAN, derived from Formula Translation) is a general-purpose, compiled imperative programming language that is especially suited to numeric computation and scientific computing. Fortran_sentence_0

Originally developed by IBM in the 1950s for scientific and engineering applications, FORTRAN came to subsequently dominate scientific computing. Fortran_sentence_1

It has been in use for over six decades in computationally intensive areas such as numerical weather prediction, finite element analysis, computational fluid dynamics, geophysics, computational physics, crystallography and computational chemistry. Fortran_sentence_2

It is a popular language for high-performance computing and is used for programs that benchmark and rank the world's fastest supercomputers. Fortran_sentence_3

Fortran encompasses a lineage of versions, each of which evolved to add extensions to the language while usually retaining compatibility with prior versions. Fortran_sentence_4

Successive versions have added support for structured programming and processing of character-based data (FORTRAN 77), array programming, modular programming and generic programming (Fortran 90), high performance Fortran (Fortran 95), object-oriented programming (Fortran 2003), concurrent programming (Fortran 2008), and native parallel computing capabilities (Coarray Fortran 2008/2018). Fortran_sentence_5

Fortran's design was the basis for many other programming languages. Fortran_sentence_6

Amongst the better-known is BASIC, which is based on FORTRAN II with a number of syntax cleanups, notably better logical structures, and other changes to work more easily in an interactive environment. Fortran_sentence_7

Naming Fortran_section_0

The names of earlier versions of the language through FORTRAN 77 were conventionally spelled in all-capitals (FORTRAN 77 was the last version in which the use of lowercase letters in keywords was strictly non-standard). Fortran_sentence_8

The capitalization has been dropped in referring to newer versions beginning with Fortran 90. Fortran_sentence_9

The official language standards now refer to the language as "Fortran" rather than all-caps "FORTRAN". Fortran_sentence_10

History Fortran_section_1

In late 1953, John W. Backus submitted a proposal to his superiors at IBM to develop a more practical alternative to assembly language for programming their IBM 704 mainframe computer. Fortran_sentence_11

Backus' historic FORTRAN team consisted of programmers Richard Goldberg, Sheldon F. Best, Harlan Herrick, Peter Sheridan, Roy Nutt, Robert Nelson, Irving Ziller, Harold Stern, Lois Haibt, and David Sayre. Fortran_sentence_12

Its concepts included easier entry of equations into a computer, an idea developed by J. Fortran_sentence_13 Halcombe Laning and demonstrated in the Laning and Zierler system of 1952. Fortran_sentence_14

Some of these programmers were chess players and were chosen to work at IBM with the thought being that they had logical minds. Fortran_sentence_15

A draft specification for The IBM Mathematical Formula Translating System was completed by November 1954. Fortran_sentence_16

The first manual for FORTRAN appeared in October 1956, with the first FORTRAN compiler delivered in April 1957. Fortran_sentence_17

This was the first optimizing compiler, because customers were reluctant to use a high-level programming language unless its compiler could generate code with performance approaching that of hand-coded assembly language. Fortran_sentence_18

While the community was skeptical that this new method could possibly outperform hand-coding, it reduced the number of programming statements necessary to operate a machine by a factor of 20, and quickly gained acceptance. Fortran_sentence_19

John Backus said during a 1979 interview with Think, the IBM employee magazine, "Much of my work has come from being lazy. Fortran_sentence_20

I didn't like writing programs, and so, when I was working on the IBM 701, writing programs for computing missile trajectories, I started work on a programming system to make it easier to write programs." Fortran_sentence_21

The language was widely adopted by scientists for writing numerically intensive programs, which encouraged compiler writers to produce compilers that could generate faster and more efficient code. Fortran_sentence_22

The inclusion of a complex number data type in the language made Fortran especially suited to technical applications such as electrical engineering. Fortran_sentence_23

By 1960, versions of FORTRAN were available for the IBM 709, 650, 1620, and 7090 computers. Fortran_sentence_24

Significantly, the increasing popularity of FORTRAN spurred competing computer manufacturers to provide FORTRAN compilers for their machines, so that by 1963 over 40 FORTRAN compilers existed. Fortran_sentence_25

For these reasons, FORTRAN is considered to be the first widely used cross-platform programming language. Fortran_sentence_26

The development of Fortran paralleled the early evolution of compiler technology, and many advances in the theory and design of compilers were specifically motivated by the need to generate efficient code for Fortran programs. Fortran_sentence_27

The most comprehensive account of Fortran history in a single document is given by Lorenzo in the book listed below. Fortran_sentence_28

FORTRAN Fortran_section_2

The initial release of FORTRAN for the IBM 704 contained 32 statements, including: Fortran_sentence_29

Fortran_unordered_list_0

  • DIMENSION and EQUIVALENCE statementsFortran_item_0_0
  • Assignment statementsFortran_item_0_1
  • Three-way arithmetic IF statement, which passed control to one of three locations in the program depending on whether the result of the arithmetic statement was negative, zero, or positiveFortran_item_0_2
  • IF statements for checking exceptions (ACCUMULATOR OVERFLOW, QUOTIENT OVERFLOW, and DIVIDE CHECK); and IF statements for manipulating sense switches and sense lightsFortran_item_0_3
  • GO TO, computed GO TO, ASSIGN, and assigned GO TOFortran_item_0_4
  • DO loopsFortran_item_0_5
  • Formatted I/O: FORMAT, READ, READ INPUT TAPE, WRITE, WRITE OUTPUT TAPE, PRINT, and PUNCHFortran_item_0_6
  • Unformatted I/O: READ TAPE, READ DRUM, WRITE TAPE, and WRITE DRUMFortran_item_0_7
  • Other I/O: END FILE, REWIND, and BACKSPACEFortran_item_0_8
  • PAUSE, STOP, and CONTINUEFortran_item_0_9
  • FREQUENCY statement (for providing optimization hints to the compiler).Fortran_item_0_10

The arithmetic IF statement was reminiscent of (but not readily implementable by) a three-way comparison instruction (CAS—Compare Accumulator with Storage) available on the 704. Fortran_sentence_30

The statement provided the only way to compare numbers—by testing their difference, with an attendant risk of overflow. Fortran_sentence_31

This deficiency was later overcome by "logical" facilities introduced in FORTRAN IV. Fortran_sentence_32

The FREQUENCY statement was used originally (and optionally) to give branch probabilities for the three branch cases of the arithmetic IF statement. Fortran_sentence_33

The first FORTRAN compiler used this weighting to perform at compile time a Monte Carlo simulation of the generated code, the results of which were used to optimize the placement of basic blocks in memory—a very sophisticated optimization for its time. Fortran_sentence_34

The Monte Carlo technique is documented in Backus et al. Fortran_sentence_35

's paper on this original implementation, The FORTRAN Automatic Coding System: Fortran_sentence_36

Many years later, the FREQUENCY statement had no effect on the code, and was treated as a comment statement, since the compilers no longer did this kind of compile-time simulation. Fortran_sentence_37

A similar fate has befallen compiler hints in several other programming languages, e.g. the register keyword in C. Fortran_sentence_38

The first FORTRAN compiler reported diagnostic information by halting the program when an error was found and outputting an error code on its console. Fortran_sentence_39

That code could be looked up by the programmer in an error messages table in the operator's manual, providing them with a brief description of the problem. Fortran_sentence_40

Later, an error-handling subroutine to handle user errors such as division by zero, developed by NASA, was incorporated, informing users of which line of code contained the error. Fortran_sentence_41

Fixed layout and punched cards Fortran_section_3

Further information: Computer programming in the punched card era Fortran_sentence_42

Before the development of disk files, text editors and terminals, programs were most often entered on a keypunch keyboard onto 80-column punched cards, one line to a card. Fortran_sentence_43

The resulting deck of cards would be fed into a card reader to be compiled. Fortran_sentence_44

Punched card codes included no lower-case letters or many special characters, and special versions of the IBM 026 keypunch were offered that would correctly print the re-purposed special characters used in FORTRAN. Fortran_sentence_45

Reflecting punched card input practice, Fortran programs were originally written in a fixed-column format, with the first 72 columns read into twelve 36-bit words. Fortran_sentence_46

A letter "C" in column 1 caused the entire card to be treated as a comment and ignored by the compiler. Fortran_sentence_47

Otherwise, the columns of the card were divided into four fields: Fortran_sentence_48

Fortran_unordered_list_1

  • 1 to 5 were the label field: a sequence of digits here was taken as a label for use in DO or control statements such as GO TO and IF, or to identify a FORMAT statement referred to in a WRITE or READ statement. Leading zeros are ignored and 0 is not a valid label number.Fortran_item_1_11
  • 6 was a continuation field: a character other than a blank or a zero here caused the card to be taken as a continuation of the statement on the prior card. The continuation cards were usually numbered 1, 2, etc. and the starting card might therefore have zero in its continuation column—which is not a continuation of its preceding card.Fortran_item_1_12
  • 7 to 72 served as the statement field.Fortran_item_1_13
  • 73 to 80 were ignored (the IBM 704's card reader only used 72 columns).Fortran_item_1_14

Columns 73 to 80 could therefore be used for identification information, such as punching a sequence number or text, which could be used to re-order cards if a stack of cards was dropped; though in practice this was reserved for stable, production programs. Fortran_sentence_49

An IBM 519 could be used to copy a program deck and add sequence numbers. Fortran_sentence_50

Some early compilers, e.g., the IBM 650's, had additional restrictions due to limitations on their card readers. Fortran_sentence_51

Keypunches could be programmed to tab to column 7 and skip out after column 72. Fortran_sentence_52

Later compilers relaxed most fixed-format restrictions, and the requirement was eliminated in the Fortran 90 standard. Fortran_sentence_53

Within the statement field, whitespace characters (blanks) were ignored outside a text literal. Fortran_sentence_54

This allowed omitting spaces between tokens for brevity or including spaces within identifiers for clarity. Fortran_sentence_55

For example, AVG OF X was a valid identifier, equivalent to AVGOFX, and 101010DO101I=1,101 was a valid statement, equivalent to 10101 DO 101 I = 1, 101 because the zero in column 6 is treated as if it were a space (! Fortran_sentence_56

), while 101010DO101I=1.101 was instead 10101 DO101I = 1.101, the assignment of 1.101 to a variable called DO101I. Fortran_sentence_57

Note the slight visual difference between a comma and a period. Fortran_sentence_58

Hollerith strings, originally allowed only in FORMAT and DATA statements, were prefixed by a character count and the letter H (e.g., 26HTHIS IS ALPHANUMERIC DATA. Fortran_sentence_59

), allowing blanks to be retained within the character string. Fortran_sentence_60

Miscounts were a problem. Fortran_sentence_61

FORTRAN II Fortran_section_4

IBM's FORTRAN II appeared in 1958. Fortran_sentence_62

The main enhancement was to support procedural programming by allowing user-written subroutines and functions which returned values with parameters passed by reference. Fortran_sentence_63

The COMMON statement provided a way for subroutines to access common (or global) variables. Fortran_sentence_64

Six new statements were introduced: Fortran_sentence_65

Fortran_unordered_list_2

  • SUBROUTINE, FUNCTION, and ENDFortran_item_2_15
  • CALL and RETURNFortran_item_2_16
  • COMMONFortran_item_2_17

Over the next few years, FORTRAN II would also add support for the DOUBLE PRECISION and COMPLEX data types. Fortran_sentence_66

Early FORTRAN compilers supported no recursion in subroutines. Fortran_sentence_67

Early computer architectures supported no concept of a stack, and when they did directly support subroutine calls, the return location was often stored in one fixed location adjacent to the subroutine code (e.g. the IBM 1130) or a specific machine register (IBM 360 et seq), which only allows recursion if a stack is maintained by software and the return address is stored on the stack before the call is made and restored after the call returns. Fortran_sentence_68

Although not specified in FORTRAN 77, many F77 compilers supported recursion as an option, and the Burroughs mainframes, designed with recursion built-in, did so by default. Fortran_sentence_69

It became a standard in Fortran 90 via the new keyword RECURSIVE. Fortran_sentence_70

Simple FORTRAN II program Fortran_section_5

This program, for Heron's formula, reads data on a tape reel containing three 5-digit integers A, B, and C as input. Fortran_sentence_71

There are no "type" declarations available: variables whose name starts with I, J, K, L, M, or N are "fixed-point" (i.e. integers), otherwise floating-point. Fortran_sentence_72

Since integers are to be processed in this example, the names of the variables start with the letter "I". Fortran_sentence_73

The name of a variable must start with a letter and can continue with both letters and digits, up to a limit of six characters in FORTRAN II. Fortran_sentence_74

If A, B, and C cannot represent the sides of a triangle in plane geometry, then the program's execution will end with an error code of "STOP 1". Fortran_sentence_75

Otherwise, an output line will be printed showing the input values for A, B, and C, followed by the computed AREA of the triangle as a floating-point number occupying ten spaces along the line of output and showing 2 digits after the decimal point, the .2 in F10.2 of the FORMAT statement with label 601. Fortran_sentence_76

FORTRAN III Fortran_section_6

IBM also developed a FORTRAN III in 1958 that allowed for inline assembly code among other features; however, this version was never released as a product. Fortran_sentence_77

Like the 704 FORTRAN and FORTRAN II, FORTRAN III included machine-dependent features that made code written in it unportable from machine to machine. Fortran_sentence_78

Early versions of FORTRAN provided by other vendors suffered from the same disadvantage. Fortran_sentence_79

IBM 1401 FORTRAN Fortran_section_7

FORTRAN was provided for the IBM 1401 computer by an innovative 63-phase compiler that ran entirely in its core memory of only 8000 (six-bit) characters. Fortran_sentence_80

The compiler could be run from tape, or from a 2200-card deck; it used no further tape or disk storage. Fortran_sentence_81

It kept the program in memory and loaded overlays that gradually transformed it, in place, into executable form, as described by Haines. Fortran_sentence_82

This article was reprinted, edited, in both editions of Anatomy of a Compiler and in the IBM manual "Fortran Specifications and Operating Procedures, IBM 1401". Fortran_sentence_83

The executable form was not entirely machine language; rather, floating-point arithmetic, sub-scripting, input/output, and function references were interpreted, preceding UCSD Pascal P-code by two decades. Fortran_sentence_84

IBM later provided a FORTRAN IV compiler for the 1400 series of computers. Fortran_sentence_85

FORTRAN IV Fortran_section_8

IBM began development of FORTRAN IV starting in 1961, as a result of customer demands. Fortran_sentence_86

FORTRAN IV removed the machine-dependent features of FORTRAN II (such as READ INPUT TAPE), while adding new features such as a LOGICAL data type, logical Boolean expressions and the logical IF statement as an alternative to the arithmetic IF statement. Fortran_sentence_87

FORTRAN IV was eventually released in 1962, first for the IBM 7030 ("Stretch") computer, followed by versions for the IBM 7090, IBM 7094, and later for the IBM 1401 in 1966. Fortran_sentence_88

By 1965, FORTRAN IV was supposed to be compliant with the standard being developed by the American Standards Association X3.4.3 FORTRAN Working Group. Fortran_sentence_89

Between 1966 and 1968, IBM offered several FORTRAN IV compilers for its System/360, each named by letters that indicated the minimum amount of memory the complier needed to run. Fortran_sentence_90

The letters (F, G, H) matched the codes used with System/360 model numbers to indicate memory size, each letter increment being a factor of two larger: Fortran_sentence_91

Fortran_unordered_list_3

  • 1966 : FORTRAN IV F for DOS/360 (64K bytes)Fortran_item_3_18
  • 1966 : FORTRAN IV G for OS/360 (128K bytes)Fortran_item_3_19
  • 1968 : FORTRAN IV H for OS/360 (256K bytes)Fortran_item_3_20

At about this time FORTRAN IV had started to become an important educational tool and implementations such as the University of Waterloo's WATFOR and WATFIV were created to simplify the complex compile and link processes of earlier compilers. Fortran_sentence_92

FORTRAN 66 Fortran_section_9

Perhaps the most significant development in the early history of FORTRAN was the decision by the American Standards Association (now American National Standards Institute (ANSI)) to form a committee sponsored by BEMA, the Business Equipment Manufacturers Association, to develop an American Standard Fortran. Fortran_sentence_93

The resulting two standards, approved in March 1966, defined two languages, FORTRAN (based on FORTRAN IV, which had served as a de facto standard), and Basic FORTRAN (based on FORTRAN II, but stripped of its machine-dependent features). Fortran_sentence_94

The FORTRAN defined by the first standard, officially denoted X3.9-1966, became known as FORTRAN 66 (although many continued to term it FORTRAN IV, the language on which the standard was largely based). Fortran_sentence_95

FORTRAN 66 effectively became the first industry-standard version of FORTRAN. Fortran_sentence_96

FORTRAN 66 included: Fortran_sentence_97

Fortran_unordered_list_4

  • Main program, SUBROUTINE, FUNCTION, and BLOCK DATA program unitsFortran_item_4_21
  • INTEGER, REAL, DOUBLE PRECISION, COMPLEX, and LOGICAL data typesFortran_item_4_22
  • COMMON, DIMENSION, and EQUIVALENCE statementsFortran_item_4_23
  • DATA statement for specifying initial valuesFortran_item_4_24
  • Intrinsic and EXTERNAL (e.g., library) functionsFortran_item_4_25
  • Assignment statementFortran_item_4_26
  • GO TO, computed GO TO, assigned GO TO, and ASSIGN statementsFortran_item_4_27
  • Logical IF and arithmetic (three-way) IF statementsFortran_item_4_28
  • DO loop statementFortran_item_4_29
  • READ, WRITE, BACKSPACE, REWIND, and ENDFILE statements for sequential I/OFortran_item_4_30
  • FORMAT statement and assigned formatFortran_item_4_31
  • CALL, RETURN, PAUSE, and STOP statementsFortran_item_4_32
  • Hollerith constants in DATA and FORMAT statements, and as arguments to proceduresFortran_item_4_33
  • Identifiers of up to six characters in lengthFortran_item_4_34
  • Comment linesFortran_item_4_35
  • END lineFortran_item_4_36

FORTRAN 77 Fortran_section_10

After the release of the FORTRAN 66 standard, compiler vendors introduced several extensions to Standard Fortran, prompting ANSI committee X3J3 in 1969 to begin work on revising the 1966 standard, under sponsorship of CBEMA, the Computer Business Equipment Manufacturers Association (formerly BEMA). Fortran_sentence_98

Final drafts of this revised standard circulated in 1977, leading to formal approval of the new FORTRAN standard in April 1978. Fortran_sentence_99

The new standard, called FORTRAN 77 and officially denoted X3.9-1978, added a number of significant features to address many of the shortcomings of FORTRAN 66: Fortran_sentence_100

Fortran_unordered_list_5

  • Block IF and END IF statements, with optional ELSE and ELSE IF clauses, to provide improved language support for structured programmingFortran_item_5_37
  • DO loop extensions, including parameter expressions, negative increments, and zero trip countsFortran_item_5_38
  • OPEN, CLOSE, and INQUIRE statements for improved I/O capabilityFortran_item_5_39
  • Direct-access file I/OFortran_item_5_40
  • IMPLICIT statement, to override implicit conventions that undeclared variables are INTEGER if their name begins with I, J, K, L, M, or N (and REAL otherwise)Fortran_item_5_41
  • CHARACTER data type, replacing Hollerith strings with vastly expanded facilities for character input and output and processing of character-based dataFortran_item_5_42
  • PARAMETER statement for specifying constantsFortran_item_5_43
  • SAVE statement for persistent local variablesFortran_item_5_44
  • Generic names for intrinsic functions (e.g. SQRT also accepts arguments of other types, such as COMPLEX or REAL*16).Fortran_item_5_45
  • A set of intrinsics (LGE, LGT, LLE, LLT) for lexical comparison of strings, based upon the ASCII collating sequence. (These ASCII functions were demanded by the U.S. Department of Defense, in their conditional approval vote.)Fortran_item_5_46

In this revision of the standard, a number of features were removed or altered in a manner that might invalidate formerly standard-conforming programs. Fortran_sentence_101

(Removal was the only allowable alternative to X3J3 at that time, since the concept of "deprecation" was not yet available for ANSI standards.) Fortran_sentence_102

While most of the 24 items in the conflict list (see Appendix A2 of X3.9-1978) addressed loopholes or pathological cases permitted by the prior standard but rarely used, a small number of specific capabilities were deliberately removed, such as: Fortran_sentence_103

Fortran_unordered_list_6

  • Hollerith constants and Hollerith data, such as GREET = 12HHELLO THERE!Fortran_item_6_47
  • Reading into an H edit (Hollerith field) descriptor in a FORMAT specificationFortran_item_6_48
  • Overindexing of array bounds by subscriptsFortran_item_6_49
  • Transfer of control out of and back into the range of a DO loop (also known as "Extended Range")Fortran_item_6_50

Variants: Minnesota FORTRAN Fortran_section_11

Control Data Corporation computers had another version of FORTRAN 77, called Minnesota FORTRAN (MNF), designed especially for student use, with variations in output constructs, special uses of COMMON and DATA statements, optimization code levels for compiling, detailed error listings, extensive warning messages, and debugging features. Fortran_sentence_104

MNF was developed by people (Liddiard & Mundstock) at the University of Minnesota. Fortran_sentence_105

MNF was available basically for free. Fortran_sentence_106

Transition to ANSI Standard Fortran Fortran_section_12

The development of a revised standard to succeed FORTRAN 77 would be repeatedly delayed as the standardization process struggled to keep up with rapid changes in computing and programming practice. Fortran_sentence_107

In the meantime, as the "Standard FORTRAN" for nearly fifteen years, FORTRAN 77 would become the historically most important dialect. Fortran_sentence_108

An important practical extension to FORTRAN 77 was the release of MIL-STD-1753 in 1978. Fortran_sentence_109

This specification, developed by the U.S. Fortran_sentence_110 Department of Defense, standardized a number of features implemented by most FORTRAN 77 compilers but not included in the ANSI FORTRAN 77 standard. Fortran_sentence_111

These features would eventually be incorporated into the Fortran 90 standard. Fortran_sentence_112

Fortran_unordered_list_7

The IEEE 1003.9 POSIX Standard, released in 1991, provided a simple means for FORTRAN 77 programmers to issue POSIX system calls. Fortran_sentence_113

Over 100 calls were defined in the document – allowing access to POSIX-compatible process control, signal handling, file system control, device control, procedure pointing, and stream I/O in a portable manner. Fortran_sentence_114

Fortran 90 Fortran_section_13

The much-delayed successor to FORTRAN 77, informally known as Fortran 90 (and prior to that, Fortran 8X), was finally released as ISO/IEC standard 1539:1991 in 1991 and an ANSI Standard in 1992. Fortran_sentence_115

In addition to changing the official spelling from FORTRAN to Fortran, this major revision added many new features to reflect the significant changes in programming practice that had evolved since the 1978 standard: Fortran_sentence_116

Fortran_unordered_list_8

  • Free-form source input, also with lowercase Fortran keywordsFortran_item_8_55
  • Identifiers up to 31 characters in length (In the previous standard, it was only six characters).Fortran_item_8_56
  • Inline commentsFortran_item_8_57
  • Ability to operate on arrays (or array sections) as a whole, thus greatly simplifying math and engineering computations.Fortran_item_8_58
    • whole, partial and masked array assignment statements and array expressions, such as X(1:N)=R(1:N)*COS(A(1:N))Fortran_item_8_59
    • WHERE statement for selective array assignmentFortran_item_8_60
    • array-valued constants and expressions,Fortran_item_8_61
    • user-defined array-valued functions and array constructors.Fortran_item_8_62
  • RECURSIVE proceduresFortran_item_8_63
  • Modules, to group related procedures and data together, and make them available to other program units, including the capability to limit the accessibility to only specific parts of the module.Fortran_item_8_64
  • A vastly improved argument-passing mechanism, allowing interfaces to be checked at compile timeFortran_item_8_65
  • User-written interfaces for generic proceduresFortran_item_8_66
  • Operator overloadingFortran_item_8_67
  • Derived (structured) data typesFortran_item_8_68
  • New data type declaration syntax, to specify the data type and other attributes of variablesFortran_item_8_69
  • Dynamic memory allocation by means of the ALLOCATABLE attribute and the ALLOCATE and DEALLOCATE statementsFortran_item_8_70
  • POINTER attribute, pointer assignment, and NULLIFY statement to facilitate the creation and manipulation of dynamic data structuresFortran_item_8_71
  • Structured looping constructs, with an END DO statement for loop termination, and EXIT and CYCLE statements for terminating normal DO loop iterations in an orderly wayFortran_item_8_72
  • SELECT . . . CASE construct for multi-way selectionFortran_item_8_73
  • Portable specification of numerical precision under the user's controlFortran_item_8_74
  • New and enhanced intrinsic procedures.Fortran_item_8_75

Obsolescence and deletions Fortran_section_14

Unlike the prior revision, Fortran 90 removed no features. Fortran_sentence_117

Any standard-conforming FORTRAN 77 program is also standard-conforming under Fortran 90, and either standard should be usable to define its behavior. Fortran_sentence_118

A small set of features were identified as "obsolescent" and expected to be removed in a future standard. Fortran_sentence_119

All of the functionalities of these early version features are performed by new Fortran 95 features. Fortran_sentence_120

Some are kept to simplify porting of old programs but may eventually be deleted. Fortran_sentence_121

Fortran_table_general_1

Obsolescent featureFortran_header_cell_1_0_0 ExampleFortran_header_cell_1_0_1 Status/fate in Fortran 95Fortran_header_cell_1_0_2
Arithmetic IF-statementFortran_cell_1_1_0 IF (X) 10, 20, 30Fortran_cell_1_1_1 DeprecatedFortran_cell_1_1_2
Non-integer DO parameters or control variablesFortran_cell_1_2_0 DO 9 X= 1.7, 1.6, -0.1Fortran_cell_1_2_1 DeletedFortran_cell_1_2_2
Shared DO-loop termination or

termination with a statement other than END DO or CONTINUEFortran_cell_1_3_0

DO 9 J= 1, 10
         DO 9 K= 1, 10
 9       L=  J + KFortran_cell_1_3_1
DeprecatedFortran_cell_1_3_2
Branching to END IF

from outside a blockFortran_cell_1_4_0

66 GO TO 77 ; . . .
     IF (E) THEN ;     . . .
77   END IFFortran_cell_1_4_1
DeletedFortran_cell_1_4_2
Alternate returnFortran_cell_1_5_0 CALL SUBR( X, Y, *100, *200 )Fortran_cell_1_5_1 DeprecatedFortran_cell_1_5_2
PAUSE statementFortran_cell_1_6_0 PAUSE 600Fortran_cell_1_6_1 DeletedFortran_cell_1_6_2
ASSIGN statement
  and assigned GO TO statementFortran_cell_1_7_0
100 . . .
     ASSIGN 100 TO H
      . . .
     GO TO H . . .Fortran_cell_1_7_1
DeletedFortran_cell_1_7_2
Assigned statement numbers and FORMAT specifiersFortran_cell_1_8_0 ASSIGN 606 TO F ... WRITE ( 6, F )...Fortran_cell_1_8_1 DeletedFortran_cell_1_8_2
H edit descriptorsFortran_cell_1_9_0 606 FORMAT ( 9H1GOODBYE. )Fortran_cell_1_9_1 DeletedFortran_cell_1_9_2
Computed GO TO statementFortran_cell_1_10_0 GO TO (10, 20, 30, 40), indexFortran_cell_1_10_1 (obsolete)Fortran_cell_1_10_2
Statement functionsFortran_cell_1_11_0 FOIL( X, Y )= X**2 + 2*X*Y + Y**2Fortran_cell_1_11_1 (obsolete)Fortran_cell_1_11_2
DATA statements
  among executable statementsFortran_cell_1_12_0
X= 27.3
     DATA  A, B, C  / 5.0, 12.0, 13.0 /
     . . .Fortran_cell_1_12_1
(obsolete)Fortran_cell_1_12_2
CHARACTER* form of CHARACTER declarationFortran_cell_1_13_0 CHARACTER*8 STRING ! Use CHARACTER(8)Fortran_cell_1_13_1 (obsolete)Fortran_cell_1_13_2
Assumed character length functionsFortran_cell_1_14_0 CHARACTER*(*) STRINGFortran_cell_1_14_1 (obsolete)Fortran_cell_1_14_2
Fixed form source codeFortran_cell_1_15_0 Column 1 contains C or * or ! for comments.
Columns 1 through 5 for statement numbers
Any character in column 6 for continuation.
Columns 73 and up ignoredFortran_cell_1_15_1
(obsolete)Fortran_cell_1_15_2

"Hello, World!" example Fortran_section_15

Fortran 95 Fortran_section_16

"F95" redirects here. Fortran_sentence_122

For the Düsseldorf-based football club, see Fortuna Düsseldorf. Fortran_sentence_123

Main article: Fortran 95 language features Fortran_sentence_124

Fortran 95, published officially as ISO/IEC 1539-1:1997, was a minor revision, mostly to resolve some outstanding issues from the Fortran 90 standard. Fortran_sentence_125

Nevertheless, Fortran 95 also added a number of extensions, notably from the High Performance Fortran specification: Fortran_sentence_126

Fortran_unordered_list_9

  • FORALL and nested WHERE constructs to aid vectorizationFortran_item_9_76
  • User-defined PURE and ELEMENTAL proceduresFortran_item_9_77
  • Default initialization of derived type components, including pointer initializationFortran_item_9_78
  • Expanded the ability to use initialization expressions for data objectsFortran_item_9_79
  • Initialization of pointers to NULL()Fortran_item_9_80
  • Clearly defined that ALLOCATABLE arrays are automatically deallocated when they go out of scope.Fortran_item_9_81

A number of intrinsic functions were extended (for example a dim argument was added to the maxloc intrinsic). Fortran_sentence_127

Several features noted in Fortran 90 to be "obsolescent" were removed from Fortran 95: Fortran_sentence_128

Fortran_unordered_list_10

  • DO statements using REAL and DOUBLE PRECISION index variablesFortran_item_10_82
  • Branching to an END IF statement from outside its blockFortran_item_10_83
  • PAUSE statementFortran_item_10_84
  • ASSIGN and assigned GO TO statement, and assigned format specifiersFortran_item_10_85
  • H Hollerith edit descriptor.Fortran_item_10_86

An important supplement to Fortran 95 was the ISO technical report TR-15581: Enhanced Data Type Facilities, informally known as the Allocatable TR. Fortran_sentence_129

This specification defined enhanced use of ALLOCATABLE arrays, prior to the availability of fully Fortran 2003-compliant Fortran compilers. Fortran_sentence_130

Such uses include ALLOCATABLE arrays as derived type components, in procedure dummy argument lists, and as function return values. Fortran_sentence_131

(ALLOCATABLE arrays are preferable to POINTER-based arrays because ALLOCATABLE arrays are guaranteed by Fortran 95 to be deallocated automatically when they go out of scope, eliminating the possibility of memory leakage. Fortran_sentence_132

In addition, elements of allocatable arrays are contiguous, and aliasing is not an issue for optimization of array references, allowing compilers to generate faster code than in the case of pointers.) Fortran_sentence_133

Another important supplement to Fortran 95 was the ISO technical report TR-15580: Floating-point exception handling, informally known as the IEEE TR. Fortran_sentence_134

This specification defined support for IEEE floating-point arithmetic and floating point exception handling. Fortran_sentence_135

Conditional compilation and varying length strings Fortran_section_17

In addition to the mandatory "Base language" (defined in ISO/IEC 1539-1 : 1997), the Fortran 95 language also includes two optional modules: Fortran_sentence_136

Fortran_unordered_list_11

  • Varying length character strings (ISO/IEC 1539-2 : 2000)Fortran_item_11_87
  • Conditional compilation (ISO/IEC 1539-3 : 1998)Fortran_item_11_88

which, together, compose the multi-part International Standard (ISO/IEC 1539). Fortran_sentence_137

According to the standards developers, "the optional parts describe self-contained features which have been requested by a substantial body of users and/or implementors, but which are not deemed to be of sufficient generality for them to be required in all standard-conforming Fortran compilers." Fortran_sentence_138

Nevertheless, if a standard-conforming Fortran does provide such options, then they "must be provided in accordance with the description of those facilities in the appropriate Part of the Standard". Fortran_sentence_139

Fortran 2003 Fortran_section_18

Fortran 2003, officially published as ISO/IEC 1539-1:2004, is a major revision introducing many new features. Fortran_sentence_140

A comprehensive summary of the new features of Fortran 2003 is available at the Fortran Working Group (ISO/IEC JTC1/SC22/WG5) official Web site. Fortran_sentence_141

From that article, the major enhancements for this revision include: Fortran_sentence_142

Fortran_unordered_list_12

  • Derived type enhancements: parameterized derived types, improved control of accessibility, improved structure constructors, and finalizersFortran_item_12_89
  • Object-oriented programming support: type extension and inheritance, polymorphism, dynamic type allocation, and type-bound procedures, providing complete support for abstract data typesFortran_item_12_90
  • Data manipulation enhancements: allocatable components (incorporating TR 15581), deferred type parameters, VOLATILE attribute, explicit type specification in array constructors and allocate statements, pointer enhancements, extended initialization expressions, and enhanced intrinsic proceduresFortran_item_12_91
  • Input/output enhancements: asynchronous transfer, stream access, user specified transfer operations for derived types, user specified control of rounding during format conversions, named constants for preconnected units, the FLUSH statement, regularization of keywords, and access to error messagesFortran_item_12_92
  • Procedure pointersFortran_item_12_93
  • Support for IEEE floating-point arithmetic and floating point exception handling (incorporating TR 15580)Fortran_item_12_94
  • Interoperability with the C programming languageFortran_item_12_95
  • Support for international usage: access to ISO 10646 4-byte characters and choice of decimal or comma in numeric formatted input/outputFortran_item_12_96
  • Enhanced integration with the host operating system: access to command line arguments, environment variables, and processor error messagesFortran_item_12_97

An important supplement to Fortran 2003 was the ISO technical report TR-19767: Enhanced module facilities in Fortran. Fortran_sentence_143

This report provided sub-modules, which make Fortran modules more similar to Modula-2 modules. Fortran_sentence_144

They are similar to Ada private child sub-units. Fortran_sentence_145

This allows the specification and implementation of a module to be expressed in separate program units, which improves packaging of large libraries, allows preservation of trade secrets while publishing definitive interfaces, and prevents compilation cascades. Fortran_sentence_146

Fortran 2008 Fortran_section_19

ISO/IEC 1539-1:2010, informally known as Fortran 2008, was approved in September 2010. Fortran_sentence_147

As with Fortran 95, this is a minor upgrade, incorporating clarifications and corrections to Fortran 2003, as well as introducing some new capabilities. Fortran_sentence_148

The new capabilities include: Fortran_sentence_149

Fortran_unordered_list_13

  • Sub-modules—additional structuring facilities for modules; supersedes ISO/IEC TR 19767:2005Fortran_item_13_98
  • Coarray Fortran—a parallel execution modelFortran_item_13_99
  • The DO CONCURRENT construct—for loop iterations with no interdependenciesFortran_item_13_100
  • The CONTIGUOUS attribute—to specify storage layout restrictionsFortran_item_13_101
  • The BLOCK construct—can contain declarations of objects with construct scopeFortran_item_13_102
  • Recursive allocatable components—as an alternative to recursive pointers in derived typesFortran_item_13_103

The Final Draft international Standard (FDIS) is available as document N1830. Fortran_sentence_150

A supplement to Fortran 2008 is the International Organization for Standardization (ISO) Technical Specification (TS) 29113 on Further Interoperability of Fortran with C, which has been submitted to ISO in May 2012 for approval. Fortran_sentence_151

The specification adds support for accessing the array descriptor from C and allows ignoring the type and rank of arguments. Fortran_sentence_152

Fortran 2018 Fortran_section_20

The latest revision of the language (Fortran 2018) was earlier referred to as Fortran 2015. Fortran_sentence_153

It is a significant revision and was released on November 28, 2018. Fortran_sentence_154

Fortran 2018 incorporates two previously published Technical Specifications: Fortran_sentence_155

Fortran_unordered_list_14

  • ISO/IEC TS 29113:2012 Further Interoperability with CFortran_item_14_104
  • ISO/IEC TS 18508:2015 Additional Parallel Features in FortranFortran_item_14_105

Additional changes and new features include support for ISO/IEC/IEEE 60559:2011 (the version of the IEEE floating point standard before the latest minor revision IEEE 754-2019), hexadecimal input/output, IMPLICIT NONE enhancements and other changes. Fortran_sentence_156

Science and engineering Fortran_section_21

Although a 1968 journal article by the authors of BASIC already described FORTRAN as "old-fashioned", Fortran has now been in use for several decades and there is a vast body of Fortran software in daily use throughout the scientific and engineering communities. Fortran_sentence_157

Jay Pasachoff wrote in 1984 that "physics and astronomy students simply have to learn FORTRAN. Fortran_sentence_158

So much exists in FORTRAN that it seems unlikely that scientists will change to Pascal, Modula-2, or whatever." Fortran_sentence_159

In 1993, Cecil E. Leith called FORTRAN the "mother tongue of scientific computing", adding that its replacement by any other possible language "may remain a forlorn hope". Fortran_sentence_160

It is the primary language for some of the most intensive super-computing tasks, such as in astronomy, climate modeling, computational chemistry, computational economics, computational fluid dynamics, computational physics, data analysis, hydrological modeling, numerical linear algebra and numerical libraries (LAPACK, IMSL and NAG), optimization, satellite simulation, structural engineering, and weather prediction. Fortran_sentence_161

Many of the floating-point benchmarks to gauge the performance of new computer processors, such as the floating-point components of the SPEC benchmarks (e.g., , ) are written in Fortran. Fortran_sentence_162

Apart from this, more modern codes in computational science generally use large program libraries, such as METIS for graph partitioning, PETSc or Trilinos for linear algebra capabilities, DUNE or FEniCS for mesh and finite element support, and other generic libraries. Fortran_sentence_163

Since the early 2000s, many of the widely used support libraries have also been implemented in C and more recently, in C++. Fortran_sentence_164

On the other hand, high-level languages such as MATLAB, Python, and R have become popular in particular areas of computational science. Fortran_sentence_165

Consequently, a growing fraction of scientific programs is also written in such higher-level scripting languages. Fortran_sentence_166

For this reason, facilities for inter-operation with C were added to Fortran 2003 and enhanced by the ISO/IEC technical specification 29113, which was incorporated into Fortran 2018 to allow more flexible interoperation with other programming languages. Fortran_sentence_167

Software for NASA probes Voyager 1 and Voyager 2 was originally written in FORTRAN 5, and later ported to FORTRAN 77. Fortran_sentence_168

As of 25 September 2013, some of the software is still written in Fortran and some has been ported to C. Fortran_sentence_169

Language features Fortran_section_22

The precise characteristics and syntax of Fortran 95 are discussed in Fortran 95 language features. Fortran_sentence_170

Portability Fortran_section_23

Portability was a problem in the early days because there was no agreed upon standard—not even IBM's reference manual—and computer companies vied to differentiate their offerings from others by providing incompatible features. Fortran_sentence_171

Standards have improved portability. Fortran_sentence_172

The 1966 standard provided a reference syntax and semantics, but vendors continued to provide incompatible extensions. Fortran_sentence_173

Although careful programmers were coming to realize that use of incompatible extensions caused expensive portability problems, and were therefore using programs such as The PFORT Verifier, it was not until after the 1977 standard, when the National Bureau of Standards (now NIST) published FIPS PUB 69, that processors purchased by the U.S. Government were required to diagnose extensions of the standard. Fortran_sentence_174

Rather than offer two processors, essentially every compiler eventually had at least an option to diagnose extensions. Fortran_sentence_175

Incompatible extensions were not the only portability problem. Fortran_sentence_176

For numerical calculations, it is important to take account of the characteristics of the arithmetic. Fortran_sentence_177

This was addressed by Fox et al. Fortran_sentence_178

in the context of the 1966 standard by the PORT library. Fortran_sentence_179

The ideas therein became widely used, and were eventually incorporated into the 1990 standard by way of intrinsic inquiry functions. Fortran_sentence_180

The widespread (now almost universal) adoption of the IEEE 754 standard for binary floating-point arithmetic has essentially removed this problem. Fortran_sentence_181

Access to the computing environment (e.g., the program's command line, environment variables, textual explanation of error conditions) remained a problem until it was addressed by the 2003 standard. Fortran_sentence_182

Large collections of library software that could be described as being loosely related to engineering and scientific calculations, such as graphics libraries, have been written in C, and therefore access to them presented a portability problem. Fortran_sentence_183

This has been addressed by incorporation of C interoperability into the 2003 standard. Fortran_sentence_184

It is now possible (and relatively easy) to write an entirely portable program in Fortran, even without recourse to a preprocessor. Fortran_sentence_185

Variants Fortran_section_24

Fortran 5 Fortran_section_25

Fortran 5 was marketed by Data General Corp in the late 1970s and early 1980s, for the Nova, Eclipse, and MV line of computers. Fortran_sentence_186

It had an optimizing compiler that was quite good for minicomputers of its time. Fortran_sentence_187

The language most closely resembles FORTRAN 66. Fortran_sentence_188

FORTRAN V Fortran_section_26

FORTRAN V was distributed by Control Data Corporation in 1968 for the CDC 6600 series. Fortran_sentence_189

The language was based upon FORTRAN IV. Fortran_sentence_190

Univac also offered a compiler for the 1100 series known as FORTRAN V. A spinoff of Univac Fortran V was Athena FORTRAN. Fortran_sentence_191

Fortran 6 Fortran_section_27

Fortran 6 or Visual Fortran 2001 was licensed to Compaq by Microsoft. Fortran_sentence_192

They have licensed Compaq Visual Fortran and have provided the Visual Studio 5 environment interface for Compaq v6 up to v6.1. Fortran_sentence_193

Specific variants Fortran_section_28

Vendors of high-performance scientific computers (e.g., Burroughs, Control Data Corporation (CDC), Cray, Honeywell, IBM, Texas Instruments, and UNIVAC) added extensions to Fortran to take advantage of special hardware features such as instruction cache, CPU pipelines, and vector arrays. Fortran_sentence_194

For example, one of IBM's FORTRAN compilers (H Extended IUP) had a level of optimization which reordered the machine code instructions to keep multiple internal arithmetic units busy simultaneously. Fortran_sentence_195

Another example is CFD, a special variant of FORTRAN designed specifically for the ILLIAC IV supercomputer, running at NASA's Ames Research Center. Fortran_sentence_196

IBM Research Labs also developed an extended FORTRAN-based language called VECTRAN for processing vectors and matrices. Fortran_sentence_197

Object-Oriented Fortran was an object-oriented extension of Fortran, in which data items can be grouped into objects, which can be instantiated and executed in parallel. Fortran_sentence_198

It was available for Sun, Iris, iPSC, and nCUBE, but is no longer supported. Fortran_sentence_199

Such machine-specific extensions have either disappeared over time or have had elements incorporated into the main standards. Fortran_sentence_200

The major remaining extension is OpenMP, which is a cross-platform extension for shared memory programming. Fortran_sentence_201

One new extension, Coarray Fortran, is intended to support parallel programming. Fortran_sentence_202

FOR TRANSIT for the IBM 650 Fortran_section_29

FOR TRANSIT was the name of a reduced version of the IBM 704 FORTRAN language, which was implemented for the IBM 650, using a translator program developed at Carnegie in the late 1950s. Fortran_sentence_203

The following comment appears in the IBM Reference Manual (FOR TRANSIT Automatic Coding System C28-4038, Copyright 1957, 1959 by IBM): Fortran_sentence_204

The permissible statements were: Fortran_sentence_205

Fortran_unordered_list_15

  • Arithmetic assignment statements, e.g., a = bFortran_item_15_106
  • GO to nFortran_item_15_107
  • GO TO (n1, n2, ..., nm), iFortran_item_15_108
  • IF (a) n1, n2, n3Fortran_item_15_109
  • PAUSEFortran_item_15_110
  • STOPFortran_item_15_111
  • DO n i = m1, m2Fortran_item_15_112
  • CONTINUEFortran_item_15_113
  • ENDFortran_item_15_114
  • READ n, listFortran_item_15_115
  • PUNCH n, listFortran_item_15_116
  • DIMENSION V, V, V, ...Fortran_item_15_117
  • EQUIVALENCE (a,b,c), (d,c), ...Fortran_item_15_118

Up to ten subroutines could be used in one program. Fortran_sentence_206

FOR TRANSIT statements were limited to columns 7 through 56, only. Fortran_sentence_207

Punched cards were used for input and output on the IBM 650. Fortran_sentence_208

Three passes were required to translate source code to the "IT" language, then to compile the IT statements into SOAP assembly language, and finally to produce the object program, which could then be loaded into the machine to run the program (using punched cards for data input, and outputting results onto punched cards). Fortran_sentence_209

Two versions existed for the 650s with a 2000 word memory drum: FOR TRANSIT I (S) and FOR TRANSIT II, the latter for machines equipped with indexing registers and automatic floating point decimal (bi-quinary) arithmetic. Fortran_sentence_210

Appendix A of the manual included wiring diagrams for the IBM 533 card reader/punch control panel. Fortran_sentence_211

Fortran-based languages Fortran_section_30

Prior to FORTRAN 77, a number of preprocessors were commonly used to provide a friendlier language, with the advantage that the preprocessed code could be compiled on any machine with a standard FORTRAN compiler. Fortran_sentence_212

These preprocessors would typically support structured programming, variable names longer than six characters, additional data types, conditional compilation, and even macro capabilities. Fortran_sentence_213

Popular preprocessors included FLECS, iftran, MORTRAN, SFtran, S-Fortran, Ratfor, and Ratfiv. Fortran_sentence_214

Ratfor and Ratfiv, for example, implemented a C-like language, outputting preprocessed code in standard FORTRAN 66. Fortran_sentence_215

Despite advances in the Fortran language, preprocessors continue to be used for conditional compilation and macro substitution. Fortran_sentence_216

One of the earliest versions of FORTRAN, introduced in the '60s, was popularly used in colleges and universities. Fortran_sentence_217

Developed, supported, and distributed by the University of Waterloo, WATFOR was based largely on FORTRAN IV. Fortran_sentence_218

A student using WATFOR could submit their batch FORTRAN job and, if there were no syntax errors, the program would move straight to execution. Fortran_sentence_219

This simplification allowed students to concentrate on their program's syntax and semantics, or execution logic flow, rather than dealing with submission Job Control Language (JCL), the compile/link-edit/execution successive process(es), or other complexities of the mainframe/minicomputer environment. Fortran_sentence_220

A down side to this simplified environment was that WATFOR was not a good choice for programmers needing the expanded abilities of their host processor(s), e.g., WATFOR typically had very limited access to I/O devices. Fortran_sentence_221

WATFOR was succeeded by WATFIV and its later versions. Fortran_sentence_222

(line programming) Fortran_sentence_223

LRLTRAN was developed at the Lawrence Radiation Laboratory to provide support for vector arithmetic and dynamic storage, among other extensions to support systems programming. Fortran_sentence_224

The distribution included the LTSS operating system. Fortran_sentence_225

The Fortran-95 Standard includes an optional Part 3 which defines an optional conditional compilation capability. Fortran_sentence_226

This capability is often referred to as "CoCo". Fortran_sentence_227

Many Fortran compilers have integrated subsets of the C preprocessor into their systems. Fortran_sentence_228

SIMSCRIPT is an application specific Fortran preprocessor for modeling and simulating large discrete systems. Fortran_sentence_229

The F programming language was designed to be a clean subset of Fortran 95 that attempted to remove the redundant, unstructured, and deprecated features of Fortran, such as the EQUIVALENCE statement. Fortran_sentence_230

F retains the array features added in Fortran 90, and removes control statements that were made obsolete by structured programming constructs added to both FORTRAN 77 and Fortran 90. Fortran_sentence_231

F is described by its creators as "a compiled, structured, array programming language especially well suited to education and scientific computing". Fortran_sentence_232

Lahey and Fujitsu teamed up to create Fortran for the Microsoft .NET Framework. Fortran_sentence_233

Silverfrost FTN95 is also capable of creating .NET code. Fortran_sentence_234

Code examples Fortran_section_31

Further information: Fortran_sentence_235

The following program illustrates dynamic memory allocation and array-based operations, two features introduced with Fortran 90. Fortran_sentence_236

Particularly noteworthy is the absence of DO loops and IF/THEN statements in manipulating the array; mathematical operations are applied to the array as a whole. Fortran_sentence_237

Also apparent is the use of descriptive variable names and general code formatting that conform with contemporary programming style. Fortran_sentence_238

This example computes an average over data entered interactively. Fortran_sentence_239

Humor Fortran_section_32

During the same FORTRAN standards committee meeting at which the name "FORTRAN 77" was chosen, a satirical technical proposal was incorporated into the official distribution bearing the title "Letter O Considered Harmful". Fortran_sentence_240

This proposal purported to address the confusion that sometimes arises between the letter "O" and the numeral zero, by eliminating the letter from allowable variable names. Fortran_sentence_241

However, the method proposed was to eliminate the letter from the character set entirely (thereby retaining 48 as the number of lexical characters, which the colon had increased to 49). Fortran_sentence_242

This was considered beneficial in that it would promote structured programming, by making it impossible to use the notorious GO TO statement as before. Fortran_sentence_243

(Troublesome FORMAT statements would also be eliminated.) Fortran_sentence_244

It was noted that this "might invalidate some existing programs" but that most of these "probably were non-conforming, anyway". Fortran_sentence_245

When X3J3 debated whether the minimum trip count for a DO loop should be zero or one in Fortran 77, Loren Meissner suggested a minimum trip count of two—reasoning (tongue-in-cheek) that if it was less than two then there would be no reason for a loop! Fortran_sentence_246

When assumed-length arrays were being added, there was a dispute as to the appropriate character to separate upper and lower bounds. Fortran_sentence_247

In a comment examining these arguments, Dr. Walt Brainerd penned an article entitled "Astronomy vs. Gastroenterology" because some proponents had suggested using the star or asterisk ("*"), while others favored the colon (":"). Fortran_sentence_248

In FORTRAN 77 (and most earlier versions), variable names beginning with the letters I–N had a default type of integer, while variables starting with any other letters defaulted to real, although programmers could override the defaults with an explicit declaration. Fortran_sentence_249

This led to the joke: "In Fortran, GOD is REAL (unless declared INTEGER)." Fortran_sentence_250

See also Fortran_section_33

Fortran_unordered_list_16


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Fortran.