Fortran 简明教程

Fortran - Variables

变量只不过是一个存储区域的名称，我们的程序可以对其进行操作。每个变量应该有特定的类型，它确定变量内存的大小和布局；可以在该内存内存储的值范围；以及可以应用于该变量的操作集。

A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable should have a specific type, which determines the size and layout of the variable’s memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable.

变量的名称可以由字母、数字和下划线字符组成。Fortran 中的名称必须遵循以下规则：

The name of a variable can be composed of letters, digits, and the underscore character. 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.

根据前一章中解释的基本类型，以下是有类型变量：

Based on the basic types explained in previous chapter, following are the variable types −

Sr.No

Type & Description

1

Integer It can hold only integer values.

2

Real It stores the floating point numbers.

3

Complex It is used for storing complex numbers.

4

Logical It stores logical Boolean values.

5

Character It stores characters or strings.

Variable Declaration

变量在程序（或子程序）开始时在类型声明语句中进行声明。

Variables are declared at the beginning of a program (or subprogram) in a type declaration statement.

变量声明的语法如下：

Syntax for variable declaration is as follows −

type-specifier :: variable_name

For example

integer :: total
real :: average
complex :: cx
logical :: done
character(len = 80) :: message ! a string of 80 characters

稍后，您可以将值赋给这些变量，例如：

Later you can assign values to these variables, like,

total = 20000
average = 1666.67
done = .true.
message = “A big Hello from Tutorials Point”
cx = (3.0, 5.0) ! cx = 3.0 + 5.0i

您还可以使用内在函数 cmplx, 将值赋给复变量：

You can also use the intrinsic function cmplx, to assign values to a complex variable −

cx = cmplx (1.0/2.0, -7.0) ! cx = 0.5 – 7.0i
cx = cmplx (x, y) ! cx = x + yi

Example

以下示例演示变量声明、赋值和屏幕显示：

The following example demonstrates variable declaration, assignment and display on screen −

program variableTesting
implicit none

   ! declaring variables
   integer :: total
   real :: average
   complex :: cx
   logical :: done
   character(len=80) :: message ! a string of 80 characters

   !assigning values
   total = 20000
   average = 1666.67
   done = .true.
   message = "A big Hello from Tutorials Point"
   cx = (3.0, 5.0) ! cx = 3.0 + 5.0i

   Print *, total
   Print *, average
   Print *, cx
   Print *, done
   Print *, message

end program variableTesting

编译并执行上述代码后，将产生以下结果 −

When the above code is compiled and executed, it produces the following result −

20000
1666.67004
(3.00000000, 5.00000000 )
T
A big Hello from Tutorials Point