Fortran - Variables
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.
The name of a variable can be composed of letters, digits, and the underscore character. A name in Fortran must follow the following rules:
It cannot be longer than 31 characters.
It must be composed of alphanumeric characters (all the letters of the alphabet, and the digits 0 to 9) and underscores (_).
First character of a name must be a letter.
Names are case-insensitive.
Based on the basic types explained in previous chapter, following are the variable types:
|Integer||It can hold only integer values.|
|Real||It stores the floating point numbers.|
|Complex||It is used for storing complex numbers.|
|Logical||It stores logical Boolean values.|
|Character||It stores characters or strings.|
Variables are declared at the beginning of a program (or subprogram) in a type declaration statement.
Syntax for variable declaration is as follows:
type-specifier :: variable_name
integer :: total real :: average complex :: cx logical :: done character(len=80) :: message ! a string of 80 characters
Later you can assign values to these variables, like,
total = 20000 average = 1666.67 done = .true. message = â€œA big Hello from Tutorials Pointâ€ cx = (3.0, 5.0) ! cx = 3.0 + 5.0i
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 â€“ 7.0i cx = cmplx (x, y) ! cx = x + yi
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
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