What is Fortran?

Fortran (short for Formula Translation) is a high-level programming language that revolutionized scientific computing. Originally developed by IBM in the 1950s, it became the first widely used language for numeric and scientific computation.

While many programming languages have risen and faded, Fortran remains a core skill in high-performance computing (HPC)—a niche that powers some of the world’s most impactful and best-paid careers. Professionals fluent in modern Fortran often work in roles involving: -Climate modeling and weather prediction for space and defense agencies -Aerospace simulations used by NASA, Boeing, and SpaceX -Quantum chemistry and computational biology at cutting-edge research labs -Nuclear simulations and particle physics at CERN and national labs -Supercomputing clusters used at NVIDIA, Intel, and Top500 HPC centers -Mastering Fortran opens doors to elite research roles, internships, and industry offers—especially when combined with skills in CUDA, OpenMP, MPI, Julia, and C.

Modern Fortran (90, 95, 2003, 2008, 2018, 2023) supports structured programming, modules, recursion, array slicing, and even parallelization via OpenMP and MPI.

Learning Fortran puts you in a powerful club of people who understand low-level optimization, array math, and performance engineering.

Fixed-form vs Free-form Fortran

Fixed-form Fortran was used in earlier versions like Fortran 66 and 77, where:

Code had to be in strict columns
Line numbers were written in columns 1–5
Code started at column 7
Comments used C or * in column 1

Free-form Fortran, introduced with Fortran 90, removed these restrictions:

No column limitations
Indentation allowed
Lowercase/uppercase interchangeable
Comments start with ! anywhere on the line Free-form Fortran removes the rigid column-based structure of older Fortran versions (like Fortran 77). It lets you write readable code, use indentation, and structure your program like modern languages (Python, C, etc.).

Comparison Table

Feature	Fixed-Form (old)	Free-Form (modern)
File extension	`.f`, `.for`, `.f77`	`.f90`, `.f95`, `.f03`, `.f08`
Column-sensitive	Yes	No
Indentation allowed?	No	Yes
End statements required?	Optional	Required

✅ Why Use Free-Form Fortran?

Free-form is the modern and recommended way to write Fortran. It enables:

Cleaner syntax and indentation
Readable blocks like Python or C
Simpler debugging and maintenance
Better compatibility with modern compilers, IDEs, and version control

File Extensions for Free-Form

Use .f90, .f95, .f03, .f08, or .f18 for free-form Fortran.
Avoid .f, .for, .f77 unless you’re writing legacy, fixed-form code.

How to Set Up

To run free-form Fortran code, you need a modern compiler.
Popular choices:

Compiler	OS	Install Command
`gfortran`	Windows/Linux/Mac	`sudo apt install gfortran` or via MSYS2
`ifort`	Intel’s Compiler	Part of Intel oneAPI (free tier)
`nvfortran`	NVIDIA HPC SDK	Good for GPU + CPU Fortran

You can also use online compilers like:

Key Benefits

Use indentation like Python
Write comments anywhere with !
Lowercase and uppercase both work
You can write clean, readable code

Syntax Basics

! This is a comment
PROGRAM hello
PRINT *, "Hello, Fortran!"
END PROGRAM hello

PROGRAM hello
- PROGRAM marks the start of your program.
- hello is the name you give to your program. You can pick any valid name; it helps you (and the computer) keep things organized, especially when you have multiple programs.
- The program name must match in END PROGRAM hello (it’s a best practice, though not always enforced).
PRINT *, outputs to the console, similar to print() in Python or printf in C.
! starts a comment—everything after ! on a line is ignored by the compiler.
You do not need to worry about columns or spacing.
PROGRAM and END PROGRAM define the main block
PRINT *, prints to console (like printf or print)
! denotes a comment
No need for specific columns
Multiple spaces allowed
Lowercase or uppercase both work

Example 1: Hello World

PROGRAM hello
PRINT *, "Hello, world!"
END PROGRAM hello

Run it online here:
https://www.tutorialspoint.com/compile_fortran_online.php

Expected Output:

Hello, world!

hello in PROGRAM hello is just a name for your program. You could call it main, test, or anything you like (no spaces, must start with a letter).

Example 2: Comments and Whitespace

PROGRAM test_comments
! This is a comment
PRINT *, "Testing spacing"
PRINT *, " Spacing doesn't matter here!"
END PROGRAM test_comments

Output:

Testing spacing
Spacing doesn't matter here!

Questions

Q1. What symbol is used to start a comment in free-form Fortran?
Q2. What happens if you write Fortran keywords in lowercase (e.g., program, print)?