Fortran 简明教程

Fortran - Basic Syntax

Fortran 程序由各种程序单元组成，例如主程序、模块以及外部子程序或过程。

A Fortran program is made of a collection of program units like a main program, modules, and external subprograms or procedures.

每个程序包含一个主程序，而且可以或不可以包含其他程序单元。主程序的语法如下所示 −

Each program contains one main program and may or may not contain other program units. The syntax of the main program is as follows −

program program_name
implicit none

! type declaration statements
! executable statements

end program program_name

A Simple Program in Fortran

让我们编写一个可以添加两个数字，并打印结果的程序 −

Let’s write a program that adds two numbers and prints the result −

program addNumbers

! This simple program adds two numbers
   implicit none

! Type declarations
   real :: a, b, result

! Executable statements
   a = 12.0
   b = 15.0
   result = a + b
   print *, 'The total is ', result

end program addNumbers

当您编译和执行上述程序时，它将生成以下结果 −

When you compile and execute the above program, it produces the following result −

The total is 27.0000000

请注意 −

Please note that −

  1. All Fortran programs start with the keyword program and end with the keyword end program, followed by the name of the program.

  2. The implicit none statement allows the compiler to check that all your variable types are declared properly. You must always use implicit none at the start of every program.

  3. Comments in Fortran are started with the exclamation mark (!), as all characters after this (except in a character string) are ignored by the compiler.

  4. The print * command displays data on the screen.

  5. Indentation of code lines is a good practice for keeping a program readable.

  6. Fortran allows both uppercase and lowercase letters. Fortran is case-insensitive, except for string literals.

Basics

Fortran 的 basic character set 包含 −

The basic character set of Fortran contains −

  1. the letters A …​ Z and a …​ z

  2. the digits 0 …​ 9

  3. the underscore (_) character

  4. the special characters = : + blank - * / ( ) [ ] , . $ ' ! " % & ; < > ?

Tokens 由基本字符集中的字符组成。标记可以是关键字、标识符、常量、字符串文字或符号。

Tokens are made of characters in the basic character set. A token could be a keyword, an identifier, a constant, a string literal, or a symbol.

程序语句由标记组成。

Program statements are made of tokens.

Identifier

标识符是用来标识变量、过程或任何其他用户定义项的名称。Fortran 中的名称必须遵循以下规则 −

An identifier is a name used to identify a variable, procedure, or any other user-defined item. A name in Fortran must follow the following rules −

  1. It cannot be longer than 31 characters.

  2. It must be composed of alphanumeric characters (all the letters of the alphabet, and the digits 0 to 9) and underscores (_).

  3. First character of a name must be a letter.

  4. Names are case-insensitive

Keywords

关键字是保留给语言的特殊单词。这些保留字不能用作标识符或名称。

Keywords are special words, reserved for the language. These reserved words cannot be used as identifiers or names.

下表列出了 Fortran 关键字——

The following table, lists the Fortran keywords −

The non-I/O keywords

allocatable

allocate

assign

assignment

block data

call

case

character

common

complex

contains

continue

cycle

data

deallocate

default

do

double precision

else

else if

elsewhere

end block data

end do

end function

end if

end interface

end module

end program

end select

end subroutine

end type

end where

entry

equivalence

exit

external

function

go to

if

implicit

in

inout

integer

intent

interface

intrinsic

kind

len

logical

module

namelist

nullify

only

operator

optional

out

parameter

pause

pointer

private

program

public

real

recursive

result

return

save

select case

stop

subroutine

target

then

type

type()

use

Where

While

The I/O related keywords

backspace

close

endfile

format

inquire

open

print

read

rewind

Write