Hello world

In this part of the tutorial, we will write our first Fortran program: the ubiquitous “Hello, World!” example.

However, before we can write our program, we need to ensure that we have a Fortran compiler set up.

Fortran is a compiled language, which means that, once written, the source code must be passed through a compiler to produce a machine executable that can be run.

Compiler setup

In this tutorial, we’ll work with the free and open source GNU Fortran compiler (gfortran), which is part of the GNU Compiler Collection (GCC).

To install gfortran on Linux, use your system package manager. On macOS, you can install gfortran using Homebrew or MacPorts. On Windows, you can get native binaries here.

To check if you have gfortran setup correctly, open a terminal and run the following command:

$> gfortran --version

this should output something like:

GNU Fortran 7.5.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Hello world

Once you have set up your compiler, open a new file in your favourite code editor and enter the following:

program hello
  ! This is a comment line; it is ignored by the compiler
  print *, 'Hello, World!'
end program hello

Having saved your program to hello.f90, compile at the command line with:

$> gfortran hello.f90 -o hello

.f90 is the standard file extension for modern Fortran source files. The 90 refers to the first modern Fortran standard in 1990.

To run your compiled program:

$> ./hello
Hello, World!

Congratulations, you’ve written, compiled and run your first Fortran program! In the next part of this tutorial, we will introduce variables for storing data.