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 −
|Sr.No||Type & Description|
It can hold only integer values.
It stores the floating point numbers.
It is used for storing complex numbers.
It stores logical Boolean values.
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 = “A big Hello from Tutorials Point” 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 – 7.0i cx = cmplx (x, y) ! cx = x + yi
The following example demonstrates variable declaration, assignment and display on screen −Live Demo
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