Fortran 90编程入门指南

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"An introduction to programming in Fortran 90" 本文档是针对Fortran 90编程语言的初级教程，适用于2011年的学习者。它旨在为那些几乎没有或完全没有编程经验的人提供基础的编程知识和Fortran 90的使用方法。通过一系列示例和练习，读者将学会如何编写简单的Fortran 90程序。 Fortran 90是FORTRAN（公式翻译）语言的一个版本，它在原有的FORTRAN 77基础上进行了大量的现代化改进，引入了模块化、数组处理和面向对象编程的概念。这个教程涵盖了以下主要知识点： 1. **基本语法**: 包括变量声明、数据类型（如整型、实型、字符型等）、常量和赋值语句。 2. **控制流程**: 如条件语句（IF-THEN-ELSE）和循环结构（DO循环）用于实现程序的逻辑控制。 3. **函数与子程序**: 学习如何定义和调用内部函数以及外部子程序，理解参数传递机制。 4. **数组**: Fortran 90强化了数组处理能力，包括一维数组、多维数组和数组操作。 5. **模块(Module)**: 模块是组织代码的一种方式，可以封装变量、子程序和其他实体，提高代码的复用性和可读性。 6. **输入/输出(I/O)**: 学习如何使用格式化和非格式化的输入输出语句（如READ和WRITE）来处理数据的输入和输出。 7. **派生数据类型(Derived Data Types)**: 允许自定义复杂的数据结构，如包含数组、子程序和其他类型的组合体。 8. **并行处理**: 虽非Fortran 90的核心特性，但该版本已经为并行计算提供了初步支持，如并行循环（DO CONCURRENT）和团队（Team）概念。 9. **错误处理**: 了解如何在程序中处理错误和异常，使用ERROR STOP和STOP语句。 10. **程序结构和布局**: 掌握程序单位（Program Unit）如主程序、子程序、函数等的组织方式，以及如何使用END关键字结束每个单位。本教程还介绍了在Linux环境下工作和使用文本编辑器的基本技能，这对于初学者来说是必要的。在学习过程中，读者将逐步熟悉Fortran 90的语法和编程风格，为编写更复杂的程序打下基础。文档由Durham大学信息技术服务部门制作，基于物理系的Fortran 77课程进行改编，并遵循特定的排版规范，以帮助读者更好地理解和执行代码。学习者应按照文档中的指导进行实践，通过编写和运行实际程序来加深对知识的理解。

Guide 138: An introduction to programming in Fortran 90

NUMber etc. Early versions of Fortran used upper case only, but this is no

longer necessary and you need not follow this convention during the

course.

Like constants, variables have to have a type. Any valid constant value can

be assigned to a Fortran variable, provided that the type of the constant is

compatible with the variable's type.

At the beginning of a program you should declare each variable and its

type. The declaration is simply a statement of the variable's type and some

optional extra details such as an initial value.

If you miss out the declaration of a variable, Fortran 90 will give it a type

according to its name: undeclared variables with names beginning with the

letters I, J, K, L, M, N will be given type integer whereas all others (A to H

and O to Z) will be type real. This 'implicit typing' rule is convenient but also

causes problems, since it means that Fortran will accept any misspelled or

undeclared variables instead of warning you. This is discussed further in

section 12. To instruct Fortran to reject any variables that have not been

declared, include the line:

implicit none

before any other declarations. The implicit none statement should be used

in all of the programs in this course.

As well as using implicit none, it is strongly advised that you comply with

the naming conventions of implicit typing when naming variables. This can

be useful if (when!) you need to resolve problems in your programs.

4. How to write, process and run a program

There are four stages to creating a Fortran 90 program:

1) Create and save the program using a text editor. The file you create is

called the source code and should have a name that ends in .f90, e.g.

fred.f90.

2) Compile the code into an intermediate format, called an object file.

Compilation is done by the command gfortran. During compilation your

program is checked for syntax errors and, if none are found, a file is

created with a name ending in .o, e.g. fred.o.

3) Link the file into a final, executable form of your program. If compilation

was successful, the gfortran command will next link your program with

any libraries that it needs. If linking is successful, the object file will be

removed and an executable file will be created. The default name for

the file will be a.out, but you can also specify a name, e.g. fred.

Whereas the original source code that you typed in should normally be

understandable to any Fortran 90 compiler, the final, executable form of

your program is specific to a particular machine type.

4) Run the program.

4.1 Writing the program

In the following sections of this course, you will create a number of small

programs. To keep the files separate from the rest of your work, you might

want to create a directory now in which to store the files. Then cd to the

new directory and work from there:

Guide 138: An introduction to programming in Fortran 90

Line 12 When a running program arrives at the stop statement,

execution is terminated and the word STOP is displayed on

the screen. The STOP statement is not compulsory.

Although it is not recommended, a program may have

several STOP statements numbered STOP 1, STOP 2, etc,

at different places within the program.

Line 13 The end statement indicates the end of the program or

subprogram. It is good practice to include the name of the

program in this line, as shown.

When you have typed in the program, compile, link and run the program as

described in the next section.

4.2 Compilation and linking

Once you have created your source file mult1.f90, you can compile and

link it in one step using the gfortran command. At a Linux command

prompt, type:

gfortran -o mult1 mult1.f90

where the basic command is gfortran mult1.f90 and the option -o mult1 is

used to name the output file mult1. If you omit this option, your executable

file will be called a.out, regardless of the name of your source file.

If the compilation and linking process was successful, gfortran will run

without displaying any messages. If any errors occurred during compilation

or linking, error messages will be displayed. Go back to the text editor and

correct the errors in mult1.f90, then save, re-compile and re-link.

Once the compilation and linking have been completed successfully, you

will have an executable file called mult1.

4.3 Running the program

To run the mult1 executable, simply type its name:

mult1

If your program compiled, linked and ran first time without errors then go

back to the editor and deliberately introduce errors in order to see what

happens - e.g. try changing integer to intger in the declaration statement

and try changing i to ii in line 10. What happens if you leave this second

mistake and remove the implicit none statement? Make sure that you

remember to correct your program afterwards!

4.4 Removing old files

At the end of this first exercise you will have generated some files. The

mult1.f90 source file that you typed is useful to keep for future reference,

but you can delete the executable file mult1, which is using up space. If

you have a mult1.o file, that can be removed too. The executable and

object files can be regenerated from mult1.f90 if you need them again.

In the next exercise you will need to modify your mult1 program. Instead of

editing mult1.f90, it is a good idea to copy mult1.f90 to another file, e.g.

mult2.f90, then work on this new file. When you are developing a new

program in a series of stages it is always a good idea to take copies as you

go along and leave previous (working) versions in case your modified

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