Fortran function example

This is an example in Fortran how to make a function:

program hello
    implicit none
    integer:: square
    integer:: i
    Print  *,"write your number:"
    read   *, i
    print  *,"your number:",i
    i= square(i)
    print  *,"your result:",i
end program Hello

integer function square( a )
  implicit none
  integer  :: a
  square   = a*a
end function square

Result:

 write your number: 
4   
 your number:           4  
 your result:          16