We’ve looked at the program and module blocks that can hold our code. Now we’ll find out where to put our data.

Declaration comes first

In Fortran, every time we want to store some value in a variable, we have to explicitly declare the type and the name of the variable first. This has to happen before any other executable statement, but after imports and other declarations like the implicit none statement:

We have a basic Fortran application and a working environment to edit, compile and run it, thanks to FPM, IFX and Visual Studio Code. Let’s take a look at the structure of our very basic application.

The program keyword

The minimum amount of code for a Fortran executable is this:

program the_program
    ! Do something here
end program the_program

Comment lines start with !. To write a multi-line comment, just repeat ! at the beginning of every line.

In the previous post I included the obligatory “hello world” snippet. It would be nice if you could actually run code like that on your computer! It’s not so hard; we have very modern tooling available, and everything works equally well on Windows and Linux. The tools are freely available too.

First, install the following programs:

• Intel oneAPI Fortan Esstentials. This includes the IFX compiler.
• Fortran Package Manager (FPM). This tool is a “zero-configuration” build system which can also install and build dependencies for you.
• Visual Studio Code. We’ll use this as our editor. As far as I know there is no fully-integrated coding solution for Fortran programs. Some may use Visual Studio, some Visual Studio Code, and Jetbrains Clion may be a good option too. But none of these have solutions for all your IDE needs. After some experimenting, I think VS Code is the best option.

In a terminal, navigate to a place where you would like to create your Fortran project, and run: