Why Fortran is easy to learn

Some may think Fortran is an archaic language, and certainly not one that should be taught, but in any respects modern Fortran is an exceptionally good language to teach programming in. Certainly better than C and its idiosyncrasies. Better than Python or Julia you say? In many cases yes. Certainly things like I/O are still problematic for the novice programmer in these languages. Partially it is because modern Fortran is easy to read and comprehend, which is an important factor for the individual learning to program for the first time. The idea of introductory languages is not necessarily that they are suited to commercial endeavours, but rather that they are (i) easy to implement algorithm in, (ii) readable, and (iii) do not contain things that will confuse and bewilder.

Let’s perform the simple task of calculating the distance to the horizon. The calculation is quite simple, all that is required is the height of your eye, i.e. the distance that your eyes are off the surface of the water. The formula for calculating the distance, d, is d=√(2rh), where r is the radius of the earth (6367.45km), and h is the height of the object in metres (divided by 1000 to convert to km). So for an observer standing in a tower 42m above sea level, the distance to the horizon is d=√(2×6367.45×(42/1000)) = 23.13km. So a program to calculate this in Fortran would look like this:

program horizon
   real :: height, dist
   write(*,*) 'Height above sea level(m): '
   read(*,*) height
   dist = sqrt(2*6367.45*(height/1000.0))
   write(*,*) 'Distance to horizon = ', dist, 'km'
end program horizon

There is very little the novice programmer could not understand in this program – even without having any real notion of the syntax of Fortran. The terms read and write imply something is being input and output, the distance calculation is effectively just an equation. The only real sticking point maybe the variable declaration on the second line. The equivalent C program is somewhat more challenging.

#include <stdio.h>
#include <math.h>
int main(void)
{
   float height, dist;
   printf("Height above sea level(m): ");
   scanf("%f", &height);
   dist = sqrt(2*6367.45*(height/1000.0));
   printf("Distance to horizon = %.2fkm\n", dist);
   return 0;
}

Firstly it is four lines longer, and the only thing the same between the two programs is the equation. Two of the lines in the C program are taken up including libraries for I/O and math functions – which Fortran doesn’t require. The printf function deals with output, and is quasi-intuitive… the scanf function is not at all intuitive. What about int main(void) – muddy. What about the Python program, surely it must be better than both Fortran and C?

import math
height = float(input('Height above sea level(m): '))
dist = math.sqrt(2*6367.45*(height/1000.0))
print('Distance to horizon = ', dist, 'km')

Python dispenses with the notion of defining the “program”, allowing the algorithm to take place with little fanfare… I mean it is only 4 lines. But the math library still has to be imported. The prompt for the height is combined together with reading in the value, which is nice and compact, but the user will still question what float() is doing. And Julia?

println("Height above sea level(m): ")
height = parse(Float64, chomp(readline()))
dist = sqrt(2*6367.45*(height/1000.0))
println("Distance to horizon = ", dist, "km")

It suffers from input issues as well, chomping and parsing things – things novice programmers don’t care to know about. The commonality among all these programs is of course the calculation. The usability of a programming language is likely associated with how well it uses appropriate words to describe functions and actions, and uses symbols appropriately.