Fortran Programming Language Cheatsheet

Fortran, short for Formula Translation, is one of the oldest programming languages still in use today. Developed in the 1950s for scientific and engineering calculations, Fortran has evolved over the years and remains a crucial language in fields like numerical simulation, scientific computing, and high-performance computing. This cheatsheet serves as a quick reference guide for Fortran programming, covering key syntax and concepts.

1. Basic Structure:

PROGRAM ProgramName
  ! Declarations
  IMPLICIT NONE

  ! Main program statements

END PROGRAM ProgramName

• PROGRAM: Indicates the start of the main program.
• IMPLICIT NONE: Disables implicit typing, requiring explicit variable declarations.

2. Data Types:

INTEGER :: i, j
REAL :: x, y
CHARACTER(LEN=20) :: name
LOGICAL :: flag

• INTEGER: Integer data type.
• REAL: Floating-point data type.
• CHARACTER: Character data type.
• LOGICAL: Logical data type.

3. Arrays:

REAL, DIMENSION(3) :: vector
INTEGER, DIMENSION(3, 4) :: matrix

• Declaring one-dimensional and two-dimensional arrays.

4. Control Structures:

a. Conditional Statements:

IF (condition) THEN
  ! Code block if condition is true
ELSEIF (another_condition) THEN
  ! Code block if another condition is true
ELSE
  ! Code block if no conditions are true
END IF

b. Loops:

DO Loop:

DO i = 1, 10, 2
  ! Loop body
END DO

DO WHILE Loop:

DO WHILE (condition)
  ! Loop body
END DO

DO UNTIL Loop:

DO UNTIL (condition)
  ! Loop body
END DO

5. Subroutines and Functions:

SUBROUTINE MySubroutine(arg1, arg2)
  ! Subroutine body
END SUBROUTINE

FUNCTION MyFunction(arg1, arg2) RESULT(result)
  ! Function body
END FUNCTION

• SUBROUTINE: Used for modularizing code.
• FUNCTION: Returns a value and is often used for calculations.

6. File Handling:

OPEN(UNIT=1, FILE='data.txt', STATUS='OLD', ACTION='READ')
READ(1, *) variable1, variable2
WRITE(1, *) variable3, variable4
CLOSE(UNIT=1)

• OPEN: Opens a file.
• READ: Reads data from a file.
• WRITE: Writes data to a file.
• CLOSE: Closes a file.

7. Modules:

MODULE MyModule
  ! Module content
CONTAINS
  ! Subroutines and functions
END MODULE MyModule

• Encapsulates procedures, data, and other constructs.
• Improves code organization and reusability.

8. Advanced Concepts:

a. Pointers:

REAL, POINTER :: ptr
ALLOCATE(ptr)

• Allows dynamic memory allocation.

b. Derived Types:

TYPE :: MyType
  INTEGER :: value1
  REAL :: value2
END TYPE MyType

• Combines multiple variables into a single user-defined type.

9. Compiler Directives:

!$OMP PARALLEL DO
DO i = 1, N
  ! Parallelized loop body
END DO

• OpenMP directives for parallel programming.

10. Error Handling:

ERROR STOP 'An error occurred.'

• Stops program execution with an error message.

Fortran may seem archaic to some, but its efficiency and legacy in scientific computing make it indispensable. This cheatsheet provides a concise overview of Fortran essentials, offering a quick reference for both beginners and experienced programmers. For more in-depth learning, refer to the official Fortran documentation and explore advanced features for specialized applications.