fortran select type

Fortran has a feature called "select type" that allows you to perform different actions based on the type of a variable. This can be useful when you have a variable that can take on different types and you want to handle each type differently.

Here is an example of how you can use select type in Fortran:

program select_type_example
  implicit none
  type :: my_type
    integer :: i
    real :: r
    character(len=10) :: c
  end type my_type

  type(my_type) :: my_var

  my_var%i = 10

  select type (my_var)
    type is (integer)
      write(,) "The variable is an integer."
    type is (real)
      write(,) "The variable is a real number."
    type is (character)
      write(,) "The variable is a character."
    class default
      write(,) "The variable is of an unknown type."
  end select

end program select_type_example

In this example, we define a type called my_type with three components: i of type integer, r of type real, and c of type character. We then declare a variable my_var of type my_type and assign a value to its i component.

Next, we use the select type construct to check the type of my_var. Inside the select type block, we have several type cases:

• If the type of my_var is integer, we print "The variable is an integer."
• If the type of my_var is real, we print "The variable is a real number."
• If the type of my_var is character, we print "The variable is a character."
• If none of the above types match, we use the class default case and print "The variable is of an unknown type."

The select type construct allows you to handle different types of variables in a concise and structured manner. It can be particularly useful when dealing with polymorphic variables or when you want to perform different operations based on the type of a variable.