The general layout of a simple Fortran program includes the following components:

Fortran is not case sensitive, so end is the same as END or End.

!-----------------------------------------------------------------------
!   Description:
!       Compute the area of a circle given the radius as input.
!
!   Modification history:
!   Date        Name        Modification
!   2011-02-16  Jason Bacon Begin
!-----------------------------------------------------------------------

!-----------------------------------------------------------------------
! Main program body

program Circle_area
    use iso_fortran_env     ! Enable error_unit for error messages
    
    ! Disable implicit declarations (i-n rule)
    implicit none

    ! Constants
    real(8), parameter :: PI = 3.1415926535897932d0
    
    ! Variable definitions for main program
    real(8) :: radius, &
                        area
    
    ! Main program statements
    print *, 'What is the radius of the circle?'
    read *, radius
    if ( radius >= 0 ) then
        area = PI * radius * radius
        print *, 'The area is ', area
    else
        write(error_unit,*) 'The radius cannot be negative.'
    endif
end program

Fortran was originally designed as a line-oriented language, which means that the end of a line marks the end of a statement. Most newer languages, in contrast, are free-format, so that a single statement can span many lines, or multiple statements may be on the same line. Languages such as C, C++, and Java use a semicolon to mark the end of each statement, and line structure is completely ignored.

Fortran 90 introduced a more flexible source code format than previous versions, but still uses the end of a line to mark the end of a statement. If a particular statement is too long to fit on the screen, it can be continued on the next line by placing an ampersand (&) at the end of the line to be continued, the same way we use a backslash (\) in a shell script:

print *, 'This message is too long to fit on a single line, ', &
         'so we use the continuation character to break it up.'