Fortran Programming

Fortran continues to be used, albeit at a substantially reduced penetration, in scientific and engineering fields which required heavy numbercrunching. I am aware of continuing use in such disciplines as aerospace engineering and high energy physics (please send me others if you know of them). There are free software (Gnu) versions of Fortran 77, although none that I know of for later versions such as Fortran 90 and 95. This is most unfortunate, and refleccts the fact that most people are being trained in C/C++ now. However, it is worth pointing out that during the 1980s, the most fashionable language was Pascal, whose programmers also looked askance at the engineers still using that "dinosaur" language, Fortran! Nowadays, I never see Pascal being used for technical programming, although my experience is admittedly limited. I suspect that C/C++ has passed the stage of being just a fashion and has, in fact, replaced Fortran. But it is a fact that legacy Fortran code remains out there and continues to be upgraded and maintained for the fast number-crunching applications.

Because of the concentration on free software, this web site discusses only Fortran 77. Hopefully someday, a free version of something later will appear.

To begin...

Use a text editor (I prefer PFE) to create a new file and type the following lines:

(Be sure to start each of these lines of text in column 7, as Fortran 77 does not have free-form input the way C does.) Save the file and call it, say helloworld.f. Compile it using the DOS command

g77 -o helloworld.exe helloworld.f

This can be done using a DOS window, or we can invoke DOS commands from within the editor itself. Fortunately, graphically oriented text editors such as PFE have facilities for compiling directly within the editor environment. I will describe the procedure using PFE, but it is easily generalizable to the other editors.

First we are assuming that the directory in which the editor is working has already been designated. (In PFE, this is done by selecting the Change Directory... option in the File menu.) Next we click on the Execute menu and select the DOS Command to Window... option. Note also that the keystroke shortcut for invoking this window is to simply press the F11 key, which is what we'll do for the remainder of this explanation. Using either method, a dialog box appears, looking like this:

Note that we have typed the compiler invocation in the Command: window already. This is a basic invocation of the compiler and, as you become more proficient in using g77, you'll probably use others. This is enough to get your started, though and what it means is this:

	Compile the Fortran language input file called helloworld.f and
	produce, as output, an executable file (for your Windows box, in this case) called helloworld.exe.

Note also that we have used the DOS symbol "." to denote the present directory as the one in which the (i) the input file is to be found, and (ii) the output executable file to be placed. The "present" directory was defined using the Change Directory command above.

Note: invoking the Execute DOS Command and Capture Output dialog box using the F11 key allows the capture of the text printed in the DOS execution window which briefly appears. The resulting captured text, appearing in the CommandOutput1 window in the PFE workspace is not a DOS window. What looks like DOS command lines are not, unfortunately. You cannot type in additional DOS commands at what looks like the new DOS prompt. You'll still have to invoke the DOS command using the F11 key again.

To produce this executable now, press the OK button. You'll see a DOS window open briefly, showing the progress of the compilation process. When g77 has finished, the temporary DOS window will close and PFE will open a second window in the PFE workspace showing what happened (i.e., it has "captured the output").

No error messages were produced and we can see that an executable file was created by producing a listing of the files currently in the directory using the F11 key:

or using Windows Explorer to see:

We can now run the executable helloworld.exe by either double-clicking it in the Windows Explorer or by executing a DOS command from within PFE using the F11 key:

Press the OK button to see the result:

Congratulations! You have a working Fortran compiler running on your laptop PC!