100 Days of Code Log R1D3

Today I had learnt about the procedures and intrinsic procedures in Fortran. Basically, a procedure can be of two types

• function
• subroutine

Functions

The functions are procedures which return a value which can either be

1. Given the same name as function name in which case the syntax will be.

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integer function function_name(inputname)
	implicit none
	integer, intent(in) :: inputname
	.
	.
	function_name = 1234..
end function function_name

In this case, the return type is given before function keyword. Also, note that in fortran, values are passed by reference by default. Hence, if the input is only an input, intent(in) needs to be mentioned. Other intents are out, inout.

2. Give a separate variable name for return value

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function function_name(inputname) result(resultname)
	implicit none
	integer, intent(in) :: inputname
	integer, intent(out) :: resultname
	.
	.
	resultname = 1234..
end function function_name

Hence, the result keyword is used to specify the return value. There is a return keyword in Fortran but it only returns the control back to the caller. Hence, the result need to be assigned properly.

Also, fortran can take optional arguments. Inside the function body, these need to be declared with optional keyword.

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integer, optional, intent(in) :: somenumber

Subroutines

Subroutines do not have a return value. They are preferably used when the input values are to be modified though the same can be done in functions. The subroutines are called through

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call subroutine_name(input)

declaring a subroutine is straight forward.

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subroutine one_adder(input)
	implicit none
	integer :: input
	input = input + 1
end subroutine one_adder

Intrinsic Procedures

There are quite a few intrinsic procedures that are available in Fortran. Many of them are scientific, but few string manipulation procedures are also available.

The list of intrinsic procedures in gcc

I tried to implement the fibonacci optimization method but the current knowledge is not sufficient. Will try again once I learn more about Fortran.