Originally developed by IBM  in the s for scientific and engineering applications, FORTRAN came to dominate this area of programming early on and has been in continuous use for over six decades in computationally intensive areas such as numerical weather prediction , finite element analysis , computational fluid dynamics , computational physics , crystallography and computational chemistry.
It is a popular language for high-performance computing  and is used for programs that benchmark and rank the world's fastest supercomputers. Fortran encompasses a lineage of versions, each of which evolved to add extensions to the language while usually retaining compatibility with prior versions.
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Fortran's design was the basis for many other programming languages. The capitalization has been dropped in referring to newer versions beginning with Fortran In late , John W. Backus submitted a proposal to his superiors at IBM to develop a more practical alternative to assembly language for programming their IBM mainframe computer. Halcombe Laning and demonstrated in the Laning and Zierler system of 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.
John Backus said during a interview with Think , the IBM employee magazine, "Much of my work has come from being lazy. I didn't like writing programs, and so, when I was working on the IBM , writing programs for computing missile trajectories, I started work on a programming system to make it easier to write programs.
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.
Worksheet 5 - Arrays and I/O
The inclusion of a complex number data type in the language made Fortran especially suited to technical applications such as electrical engineering. 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.
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 The statement provided the only way to compare numbers—by testing their difference, with an attendant risk of overflow. 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.
The Monte Carlo technique is documented in Backus et al.
[Fortran Tuto 1] Hello World !
The fundamental unit of program is the basic block ; a basic block is a stretch of program which has one entry point and one exit point. The purpose of section 4 is to prepare for section 5 a table of predecessors PRED table which enumerates the basic blocks and lists for every basic block each of the basic blocks which can be its immediate predecessor in flow, together with the absolute frequency of each such basic block link. 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.
A similar fate has befallen compiler hints in several other programming languages, e. The first FORTRAN compiler reported diagnostic information by halting the program when an error was found and outputting an error code on its console. 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.
Before the development of disk files, text editors and terminals, programs were most often entered on a keypunch keyboard onto column punched cards , one line to a card. The resulting deck of cards would be fed into a card reader to be compiled.
Punched card codes included no lower-case letters or many special characters, and special versions of the IBM keypunch were offered that would correctly print the re-purposed special characters used in FORTRAN.
Reflecting punched card input practice, Fortran programs were originally written in a fixed-column format, with the first 72 columns read into twelve bit words. A letter "C" in column 1 caused the entire card to be treated as a comment and ignored by the compiler. Otherwise, the columns of the card were divided into four fields:.
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.
An IBM could be used to copy a program deck and add sequence numbers. Some early compilers, e. Later compilers relaxed most fixed-format restrictions, and the requirement was eliminated in the Fortran 90 standard. Within the statement field, whitespace characters blanks were ignored outside a text literal.
Arrays and Formatted I/O
This allowed omitting spaces between tokens for brevity or including spaces within identifiers for clarity. Note the slight visual difference between a comma and a period. Miscounts were a problem. The main enhancement was to support procedural programming by allowing user-written subroutines and functions which returned values, with parameters passed by reference.
Six new statements were introduced: . 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.
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.
This program, for Heron's formula , reads data on a tape reel containing three 5-digit integers A, B, and C as input.
Since integers are to be processed in this example, the names of the variables start with the letter "I". 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".
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.
The compiler could be run from tape, or from a card deck; it used no further tape or disk storage. It kept the program in memory and loaded overlays that gradually transformed it, in place, into executable form, as described by Haines.
In this revision of the standard, a number of features were removed or altered in a manner that might invalidate formerly standard-conforming programs. Removal was the only allowable alternative to X3J3 at that time, since the concept of " deprecation " was not yet available for ANSI standards. While most of the 24 items in the conflict list see Appendix A2 of X3. 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.
These features would eventually be incorporated into the Fortran 90 standard. The IEEE 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 standard:. Unlike the prior revision, Fortran 90 removed no features. Appendix B.
A small set of features were identified as "obsolescent" and expected to be removed in a future standard. All of the functionalities of these early version features are performed by new Fortran 95 features.
Some are kept to simplify porting of old programs but may eventually be deleted. Nevertheless, Fortran 95 also added a number of extensions, notably from the High Performance Fortran specification:.
A number of intrinsic functions were extended for example a dim argument was added to the maxloc intrinsic. 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.
This specification defined support for IEEE floating-point arithmetic and floating point exception handling. This report provided sub-modules, which make Fortran modules more similar to Modula-2 modules.
They are similar to Ada private child sub-units. 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. The new capabilities include:.
The specification adds support for accessing the array descriptor from C and allows ignoring the type and rank of arguments.
The latest revision of the language Fortran was earlier referred to as Fortran Although a 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. Leith called FORTRAN the "mother tongue of scientific computing", adding that its replacement by any other possible language "may remain a forlorn hope".
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.
Consequently, a growing fraction of scientific programs is also written in such higher-level scripting languages. The precise characteristics and syntax of Fortran 95 are discussed in Fortran 95 language features.
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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.
Standards have improved portability. The standard provided a reference syntax and semantics, but vendors continued to provide incompatible extensions. Government were required to diagnose extensions of the standard. Rather than offer two processors, essentially every compiler eventually had at least an option to diagnose extensions. Incompatible extensions were not the only portability problem.
For numerical calculations, it is important to take account of the characteristics of the arithmetic.
This was addressed by Fox et al. The widespread now almost universal adoption of the IEEE standard for binary floating-point arithmetic has essentially removed this problem. Access to the computing environment e. 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.
This has been addressed by incorporation of C interoperability into the standard. It is now possible and relatively easy to write an entirely portable program in Fortran, even without recourse to a preprocessor. It had an optimizing compiler that was quite good for minicomputers of its time.
Fortran 6 or Visual Fortran was licensed to Compaq by Microsoft. They have licensed Compaq Visual Fortran and have provided the Visual Studio 5 environment interface for Compaq v6 up to v6. Vendors of high-performance scientific computers e.
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. Such machine-specific extensions have either disappeared over time or have had elements incorporated into the main standards.
The major remaining extension is OpenMP , which is a cross-platform extension for shared memory programming. One new extension, Coarray Fortran, is intended to support parallel programming. Punched cards were used for input and output on the IBM 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.
These preprocessors would typically support structured programming , variable names longer than six characters, additional data types, conditional compilation , and even macro capabilities.