Fortran 简明教程

Fortran - Data Types

Fortran provides five intrinsic data types, however, you can derive your own data types as well. The five intrinsic types are −

  1. Integer type

  2. Real type

  3. Complex type

  4. Logical type

  5. Character type

Integer Type

The integer types can hold only integer values. The following example extracts the largest value that can be held in a usual four byte integer −

program testingInt
implicit none

   integer :: largeval
   print *, huge(largeval)

end program testingInt

当您编译并执行以上程序时，将生成以下结果——

2147483647

Note that the huge() function gives the largest number that can be held by the specific integer data type. You can also specify the number of bytes using the kind specifier. The following example demonstrates this −

program testingInt
implicit none

   !two byte integer
   integer(kind = 2) :: shortval

   !four byte integer
   integer(kind = 4) :: longval

   !eight byte integer
   integer(kind = 8) :: verylongval

   !sixteen byte integer
   integer(kind = 16) :: veryverylongval

   !default integer
   integer :: defval

   print *, huge(shortval)
   print *, huge(longval)
   print *, huge(verylongval)
   print *, huge(veryverylongval)
   print *, huge(defval)

end program testingInt

当您编译和执行上述程序时，它将生成以下结果 −

32767
2147483647
9223372036854775807
170141183460469231731687303715884105727
2147483647

Real Type

It stores the floating point numbers, such as 2.0, 3.1415, -100.876, etc.

Traditionally there are two different real types, the default real type and double precision type.

However, Fortran 90/95 provides more control over the precision of real and integer data types through the kind specifier, which we will study in the chapter on Numbers.

The following example shows the use of real data type −

program division
implicit none

   ! Define real variables
   real :: p, q, realRes

   ! Define integer variables
   integer :: i, j, intRes

   ! Assigning  values
   p = 2.0
   q = 3.0
   i = 2
   j = 3

   ! floating point division
   realRes = p/q
   intRes = i/j

   print *, realRes
   print *, intRes

end program division

当您编译并执行以上程序时，将生成以下结果——

0.666666687
0

Complex Type

This is used for storing complex numbers. A complex number has two parts, the real part and the imaginary part. Two consecutive numeric storage units store these two parts.

For example, the complex number (3.0, -5.0) is equal to 3.0 – 5.0i

We will discuss Complex types in more detail, in the Numbers chapter.

Logical Type

There are only two logical values: .true. and .false.

Character Type

The character type stores characters and strings. The length of the string can be specified by len specifier. If no length is specified, it is 1.

For example,

character (len = 40) :: name
name = “Zara Ali”

The expression, name(1:4) would give the substring “Zara”.

Implicit Typing

Older versions of Fortran allowed a feature called implicit typing, i.e., you do not have to declare the variables before use. If a variable is not declared, then the first letter of its name will determine its type.

从 i、j、k、l、m 或 n 开始的变量名，被认为是整数变量，其它是实数变量。但是，必须将所有变量声明出来，因为这是良好的编程习惯。为此，您用以下语句开始程序：

implicit none

此语句关闭隐式类型。