“Hello, world!”

Here is the “Hello, world!” example of Fortran.

program main
    implicit none
    print *, 'Hello, World!'
end program main

• Every Fortran program executes from program `name` to end program `name`, where `name` is the name of the Fortran program. “Names” (such as variable names, procedure names and module names) in Fortran must be formed by letters, digits and underscore, and must start with a letter (which means __main__ is not a valid “name”).

• implicit none bans the confusing “I-N implicit declaration rule” of Fortran. It is a good habit to add implicit none in every Fortran program, even if nothing is declared in the program.

• print makes an output to “file with unit *”, which is usually the screen. *, means that the output is in “format *”, which will be automatically determined by the processor with some restrictions of Fortran standard.