Fortran Tutorial for Beginners – Learn Fortran in simple and easy steps starting from basic to advanced concepts with examples including Overview, Environment. Fortran 77 has only one loop construct, called the do-loop. The do-loop corresponds to what is known as a for-loop in other languages. Other loop constructs. The goal of this Fortran tutorial is to give a quick introduction to the most common features of the Fortran 77 and Fortran 90 programming languages. It is not a.
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You can help by splitting this big page into smaller ones. Please make sure to follow the naming policy. Dividing books into smaller sections can provide more focus and allow each one to do one thing well, which benefits everyone. The goal of this Fortran tutorial is to give a quick introduction to the most common features of the Fortran 77 programming language. A companion tutorial introduces the key enhancements found in Fortran It is not a complete reference!
Many details have been omitted. The presentation focuses on scientific computations, mainly linear algebra. The outline of this tutorial was inspired by the book “Handbook for Matrix Computations” by T. Leestma published by Prentice Hall. Tktorial is a general purpose programming language, mainly intended for mathematical computations in e.
However, following the current trend to only capitalize the first letter in acronyms, we will call it Fortran. Fortran was the first ever high-level programming language.
The work on Fortran started in the ‘s at IBM and there have been many versions since. By convention, a Fortran version is denoted by the last two digits of the year the standard was proposed. The most common Fortran version today is still Fortran 77, although Fortran 90 is growing in popularity.
Fortran 95 is a revised version of Fortran There are also several versions of Fortran aimed at parallel computers. Users should be aware that most Fortran 77 compilers allow a superset of Fortran 77, i. Fortran is the dominant programming language used in engineering applications.
It is therefore important for engineering graduates to be able to read and modify Fortran code. From time to time, so-called experts predict that Fortran will rapidly fade in popularity and soon become extinct. These predictions have always failed.
Fortran is the most enduring computer programming language in history. One of the main reasons Fortran has survived and will survive is software inertia. Once a company has spent many man-years and perhaps millions of dollars on a software product, it is unlikely to try to translate the software to a different language.
Reliable software translation is a very difficult task. Consequently, if your program is written in ANSI Fortran 77, using nothing outside the standard, then it will run on any computer that has a Fortran f7 compiler. Thus, Fortran programs are portable across machine platforms. If you want to read some Fortran Standards Documents, click here. A Fortran program is just a sequence of lines of text.
The text has to follow a certain structure to be a valid Fortran program. We start by looking at a simple example:. The lines that begin with with a “c” are comments and have no purpose other than to make the program more readable tutoriap humans.
Originally, all Fortran programs had to be written in all upper-case letters. Most people now write lower-case since this is more legible, and so will we. You may tutoria, to mix case, but Tutorizl is not case-sensitive, so “X” and “x” are the same variable. A Fortran program generally consists of a main program or driver and possibly several subprograms procedures or subroutines.
For now we will place all the statements in the main program; subprograms will be treated later. The structure of a main program is:. In this tutorial, words that are in italics should not be taken as literal text, but rather as a description of what belongs in their place.
The stop statement is optional and may seem superfluous since the program will stop when it reaches the end anyway, but it is recommended to always terminate a program with the stop statement to emphasize that the execution flow stops there. Fortran 77 is not a free-format language, but has a very strict set of rules for how the source code should be formatted. The most important rules are the column position rules:. Most lines in a Fortran 77 program starts with 6 blanks and ends before column 72, i.
Note that many examples in this document have been slightly reformatted to improve their layout in the WIKI environment. A single space character has been added to the beginning of each code line to prevent the wiki framework from interpreting the first character as a markup command.
Empty lines terminate formatting of code examples but a single space followed by newline displays as an empty line of code and continues the example. Annoyingly, another deficiency in the wiki framework is the requirement to tack a closing element tag on to the end of the element content for elements such as pre or code to prevent an additional blank line being added to the output box.
A line that begins with the letter “c” or an asterisk in the first column is a comment. Comments uttorial appear anywhere in the program. Well-written comments are crucial to program readability. You may also encounter Fortran programs that use the exclamation mark! This is not a standard part of Fortran 77, but is supported by several Fortran 77 compilers and is explicitly allowed in Fortran When understood, the exclamation mark may appear anywhere on a line except in positions Sometimes, a statement does not fit into the 66 available columns of a single line.
One can then break the statement into two or more lines, and use the continuation mark in position 6. Any character can be used instead of the plus sign as a continuation character. Yutorial is considered good programming style to use either the plus sign, an ampersand, or digits using 2 for the second line, 3 for the third, and so on.
Fortran 77 Tutorial – Wikibooks, open books for an open world
Blank spaces are ignored in Fortran So if you remove all blanks in a Fortran 77 program, the program is still acceptable to a compiler but almost tjtorial to humans.
Variable names in Fortran consist of characters chosen from the letters a-z and the digits The first character must be a letter. Fortran 77 does not distinguish between upper and lower case, in fact, it assumes all input is upper case. However, nearly all Fortran 77 compilers will accept lower case.
If you should ever encounter tktorial Fortran 77 compiler that tutirial on upper case it is usually easy to convert the source code to all upper case. Unlike most other languages, Fortran does not have any reserved words. Although it is possible to use words that the language is built upon as variable names if the context shows that it can’t be meant as a keyword, this can become very confusing and is therefore not recommended. Every variable should be defined in a declaration.
This establishes the type of the variable. The most common declarations are:.
The list f7 variables should consist of variable names separated by commas. Each variable should be declared exactly once. If a variable is undeclared, Fortran 77 uses a set of implicit rules to establish the type.
This means all variables starting with the letters i-n are integers and all others are real.
Many old Fortran 77 programs uses these implicit rules, but you should not! The probability of errors in your program grows dramatically if you do not consistently declare your variables. Fortran 77 has only one type for integer variables. Integers are usually stored as 32 bits 4 bytes variables. Fortran 77 has two different types for floating point variables, called real and double precision.
While real is often adequate, some numerical calculations need very high precision and double precision should be used. Usually a real is a 4 byte variable and the double precision is 8 bytes, but this is machine dependent.
Some constants appear many times in a program. It is then often desirable to define them only once, in the beginning of the program. This is what the parameter statement is for. It also makes programs more readable. For example, the circle area program should rather have been written like this:.
The name defined in the parameter statement is not a variable but a constant, which means you cannot change its value later in the program. A name can appear in at most one parameter statement. The parameter statement s must come before the first executable statement. Some good reasons to use the parameter statement are:.
The simplest form of an expression is a constant. There are 6 types of constants, corresponding to the 6 data types. Here are some integer constants:. The E-notation means that you should multiply the constant by 10 raised to the power following the “E”. For constants that are larger than the largest real allowed, or that requires high precision, double precision should be used.
The notation is the same as for real constants except the “E” is replaced by a “D”. The next type is complex constants. This is designated by a pair of constants integer or realseparated by a comma and enclosed in parentheses.