Introduction to Fortran Programming

Fortran, short for “Formula Translation,” is one of the oldest high-level programming languages in existence. Developed in the 1950s by IBM, Fortran was originally designed for numeric and scientific computing. Its creation marked a significant step forward in programming because it allowed engineers, scientists, and mathematicians to express mathematical formulas in a language that could be directly executed by a computer. Before Fortran, programming was primarily done in assembly language or machine code, which was cumbersome and error-prone. Fortran introduced a more human-readable syntax, enabling more efficient problem-solving in scientific and engineering applications.

Over the decades, Fortran has evolved through several standards, including Fortran IV, Fortran 77, Fortran 90, Fortran 95, Fortran 2003, Fortran 2008, and Fortran 2018. Each standard introduced new features, such as structured programming constructs, modules, array operations, object-oriented programming, and parallel computing capabilities. Despite being over 70 years old, Fortran remains relevant in fields like computational physics, climate modeling, fluid dynamics, and numerical simulations. Its enduring popularity is largely due to its speed, efficiency, and the vast ecosystem of scientific libraries that have been built over decades.

Why Fortran is Still Relevant Today

While modern programming languages like Python, C++, and Java are widely used for general-purpose programming, Fortran continues to excel in high-performance numerical computing. One of Fortran’s major advantages is its ability to handle large-scale mathematical computations with high efficiency. Modern compilers optimize Fortran code exceptionally well, often outperforming equivalent C or C++ implementations in numerical tasks.

Many legacy scientific codes, particularly in areas like weather forecasting, aerospace simulations, and nuclear engineering, were originally written in Fortran. Rewriting these programs in other languages would be both costly and error-prone. Therefore, Fortran remains the language of choice for maintaining, updating, and extending these applications. Moreover, Fortran’s syntax and structure are designed specifically for array operations and mathematical formulas, making it an ideal tool for scientists and engineers who deal with matrices, vectors, and complex numerical algorithms on a daily basis.

Another reason for Fortran’s continued relevance is its integration with modern technologies. Fortran can interface with C libraries, Python, and parallel computing frameworks like MPI and OpenMP. This makes it possible to leverage Fortran’s computational efficiency while taking advantage of modern development tools and high-level programming environments.

Installing Fortran Compilers

Before you can start writing and running Fortran programs, you need a Fortran compiler. One of the most widely used free compilers is gfortran, which is part of the GNU Compiler Collection (GCC). gfortran is compatible with Windows, macOS, and Linux, making it accessible to a wide range of users.

Installing gfortran on Windows

1. Download the MinGW-w64 installer from the official website.
2. During installation, select the architecture (x86_64 for 64-bit systems) and the threads model (posix).
3. Complete the installation and add the bin directory to your system PATH environment variable.
4. Open a command prompt and type:

gfortran --version

If installed correctly, this will display the version of gfortran installed on your system.

Installing gfortran on macOS

1. The easiest way to install gfortran on macOS is through Homebrew. First, install Homebrew if you don’t have it:

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

2. Then install gfortran:

brew install gcc

3. Verify the installation:

gfortran --version

Installing gfortran on Linux

Most Linux distributions include gfortran in their package repositories. For example, on Ubuntu or Debian:

sudo apt update
sudo apt install gfortran

For Fedora or CentOS:

sudo dnf install gcc-gfortran

After installation, check the version:

gfortran --version

Once installed, you are ready to write and compile Fortran programs.

Writing Your First Fortran Program

A good starting point for beginners is to write a simple program that prints a message to the console. This allows you to familiarize yourself with the basic structure of a Fortran program.

Here is a simple “Hello, Fortran!” program:

program hello
print *, "Hello, Fortran!"
end program hello

Explanation of the Code

• program hello: This line defines the start of a program named hello. In Fortran, every program must have a program name.
• print *, "Hello, Fortran!": The print statement outputs the text "Hello, Fortran!" to the console. The asterisk * specifies a default formatting for the output.
• end program hello: This marks the end of the program. It is good practice to match the program name with the ending statement, although Fortran does allow a simple end as well.

Compiling and Running the Program

Once you have written your program, you need to compile it into an executable file that the computer can run. The process involves two steps: compilation and execution.

Step 1: Compile

Open your terminal or command prompt, navigate to the directory where your program is saved, and type:

gfortran hello.f90 -o hello

• hello.f90 is the name of the source file.
• -o hello specifies the name of the executable file that will be created.

If there are no syntax errors, this command will produce an executable named hello.

Step 2: Run

To run the program, type the following in the terminal:

./hello

The output should be:

Hello, Fortran!

This confirms that your Fortran environment is correctly set up and that your first program runs successfully.

Basic Input and Output in Fortran

In addition to printing messages, Fortran allows you to read input from the user using the read statement. This is useful for creating interactive programs.

Here is an example that reads a number from the user and prints it:

program input_example
integer :: number
print *, "Enter an integer:"
read *, number
print *, "You entered:", number
end program input_example

Explanation

• integer :: number: Declares a variable named number of type integer.
• print *, "Enter an integer:": Prompts the user to enter a value.
• read *, number: Reads the value entered by the user and stores it in the variable number.
• print *, "You entered:", number: Displays the entered value back to the user.

This program introduces two fundamental concepts: variables and input/output operations. Variables store data in memory, and input/output operations allow communication with the user.

Advanced Output Formatting

While print * provides basic output functionality, Fortran also supports the write statement, which allows for more control over formatting:

program formatted_output
real :: pi
pi = 3.1415926535
write(*,'(A, F10.5)') "The value of pi is: ", pi
end program formatted_output

• write(*,'(A, F10.5)') specifies the format: A for a string, F10.5 for a floating-point number with 10 total characters and 5 digits after the decimal.
• This allows you to align numbers and text neatly in your output, which is particularly important for scientific calculations and reports.