# 022. Functions should be `pure` and have `intent(in)` arguments topic: {ref}`procedures` `intent(in)` arguments cannot be changed. `pure` = no side effects. Use `subroutine` instead for a procedure with side effects. ```{literalinclude} ../../src/func.f90 :language: fortran :caption: func.f90 | |

``` ```{code-block} text :caption: Output[^gfortran-version] 12.0000000 ``` [^gfortran-version]: Compiled using `GNU Fortran (Ubuntu 11.3.0-1ubuntu1~22.04) 11.3.0` with no flags `real` in the function definition line indicates the type of the return value. By default, the value corresponding to a variable with the same name as the function is returned (here `area`). ---

Demo of a Fortran function. Intent(in) arguments
cannot be changed. Function arguments should be intent(in). Pure = no side-effects.

print*,area(3.,4.) ! 12
contains
real pure function area(length,width)
real, intent(in) :: length,width
area = length*width
end function area
end
— FortranTip (@fortrantip) December 19, 2021