Fortran Tutorial Lesson 1 | your first program

WELCOME everyone who wishes to learn FORTRAN. We will write our first FORTRAN program in the easiest way possible.

You are on this page so I guess you know the meaning of programming language. You choose to see FORTRAN programming language, I guess you know the importance of FORTRAN for the physics. So I will directly take you to write a FORTRAN code.

1. Requirements to write First FORTRAN program code

To write a FORTRAN code, you should have two things with you. The first one is a text editor and the other one is compiler.

a) Text editor

A text editor is where we write our FORTRAN code. You can use any text editor you have in your system or install a new one of your choice. I will be using Ubuntu OS default text editor gedit.

If you don’t have one, you can install gedit from its website.

Or, you can install latest version of gedit using command in terminal. Type

$sudo apt-get install gedit

b) Compiler

Compiler is a software that converts our code to the language that computer understands. It is an important tool to write any programming language.

For compiler, I will be using gfortran compiler. you can install other compiler too.

To install gfortran compiler on Ubuntu system, open up terminal using Ctrl + Shift + T and type

$sudo apt-get install gfortran

After that we are good to start our very first program:

2. Your first FORTRAN program

Like other programming language, the first thing you will learn in FORTRAN program is to display that means, to print out something in the screen.

However, there are two ways to print out on the screen in FORTRAN Programming Language. The first way to do so is by using print*, statement and other way is using write(*,*) statement.

a) Print*, Statement

The print*, statement is widely used to print out on screen. This is easier to write and remember.

b) Write(*,*) Statement

The write(*,*) statement, however, is important for other purposes also. It can be used for the output formatting as well as file handling. The two asterisks sign *, * used in write(*,*) have different meanings and hence uses. The former one is used to provide a format to the output whereas the later is used for file handling.

c) Let’s Begin

Ok, let’s start our first code. Open up gedit and type the below code. Don’t worry, for now, I will explain all those words later.

program first
  print*, "Hello World!"
end program

Then save the with the name of your choice and give extension as .f95. I will save in the name example.f95. Notice the directory (folder), where you saved the file.

Remember, FORTRAN files should have the extension of .f95 or you can use .f90, .f77 for older versions.

If you are using ubuntu system, follow the below steps otherwise you can go directly to the explaining part.

Now open terminal using Ctrl + Shift + T then go to the directory where you saved your file, and type:

$gfortran example.f95

My file name is example.f95. You have to type your file name instead of mine.

Hit enter. If it doesn’t say any error, then congratulation, your first code in FORTRAN is correct. CHEER UP!

Now if you check your folder, you will see a new file with the name a.out. This is the file created by compiler, a file that computer understands. Now we have to execute it. So type the command once again in the terminal

$./a.out

Then it gives the output. If you see the terminal, it will say:

Hello World!

If you have problems with terminal commands, here is an article for you. Read terminal basic commands.

EXPLANATION

Now let’s see our previous code and understand in detail.

program first
  print*, "Hello World!"
end program

FORTRAN main code should always lie between program and end program.

program program_name
     main code.........
     ..............
end program

Give the program name of your choice. But you should not use the reserved words for the program name. Click here to see list of reserved words.

Lets look at the line print*, "hello world". The print*, statement says to display something in the screen, we choose to display hello world text. Remember to surround text using single or double quotes.

You can change your text and and use many print*, statements, you want

program other
  print*, "I am Learning FORTRAN"
  print*, "Printing in FORTRAN is very easy."
end program

The output is:

I am learning FORTRAN
Printing in FORTRAN is very easy.

The same thing can be obtained using write(*,*) statement as well.

program other
  write(*,*) "I am Learning FORTRAN"
  write(*,*) "Printing in FORTRAN is very easy."
end program

Remember how print*, and write(*,*) statements are written.

If you want to print out the numbers, you don’t need to surround them with a double-quote. for e.g.

program numbers
print*, 45
print*, 100.34
end program

Output:

45
100.34

But if you consider number as a text, then you must use quote.

program number_and_text
print*, "I have 100 apples."
print*, "34"
end program

Output

I have 100 apples
34

Move on to next tutorial and enjoy coding.

You can view the full playlist of the FORTRAN tutorials on youtube.

If you got any problem above, You can watch this video on YouTube.