Fortran - Variables

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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
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

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

For example

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 Howcodex” 
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

Example

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 Howcodex" 
   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 Howcodex
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