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Fortran Summary
(Compiled from Hahn [1994])
• Successful problem solving with a computer requires knowledge of the coding rules and a sound logical
plan
• The compiler translates the program statements into machine code
• Fortran statements may be up to 132 characters long and may start anywhere on the line
• All statements, except assignments, start with a keyword
• A Fortran token is a sequence of characters forming a label, keyword, name, constant, operator or
separator
• Blanks should be used to improve readability, except inside keywords and names
• Comments may be typed after the exclamation! They should be used liberally to describe variables and
to explain how a program works
• A statement with & as its last non-blank character will be continued onto the next line
• There are five intrinsic data types: integer, real, complex, logical and character
• Values of each data type are represented by literal constants
• Integer constants may also be represented in binary, octal and hexadecimal
• Real constants are represented in fixed point or floating point (exponential) form
• Alphanumeric characters are the letters, digits and the underscore
• Names may contain up to 31 alphanumeric characters, starting with a letter
• A variable is the symbolic name of a memory location
• The IMPLICIT NONE statement should be used to avoid variables being given a type implicitly
• A numeric variable should be declared integer or real in a type declaration statement
• Numeric expressions may be formed from constants and variables with the five numeric intrinsic
operators, which operate according to strict rules of precedence
• Decimal parts are truncated when integers are divided, or when integers are assigned to reals
• Numeric assignment computes the value of a numeric expression and assigns it to a real or integer
variable
• Groups of variables may be given initial values in a DATA statement
• PRINT* is used to print (display) output
• READ* is used to input data from the keyboard while a program is running
• Data may also be read from an external file (e.g., a disk file)
References
Hahn, B.D., Fortran 90 for Scientist and Engineers, Butterworth-Heinemann, Woburn, MA, 1994.