Fortran Elements and Concepts

This section provides definitions for the various elements of a Fortran program. The Fortran language is written using a specific set of characters that form the words, numbers, names, and expressions that make up Fortran statements. These statements form a Fortran program. The Fortran character set, the rules for writing Fortran statements, the main structural elements of a program, and the proper order of statements in a program are also discussed in this section.

The Fortran character set consists of 26 uppercase and 26 lowercase letters (alphabetic characters), the numbers 0 through 9 (digits), and special characters. This manual refers to letters (uppercase and lowercase) together with the underscore (_) as extended alphabetic characters. The extended alphabetic characters together with the digits are also referred to as alphanumeric characters. The complete character set is

Letters: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
a b c d e f g h i j k l m n o p q r s t u v w x y z

Digits: 0 1 2 3 4 5 6 7 8 9

Special Characters:
Blank
=          Equal
+          Plus
-          Minus
*          Asterisk
/          Slash
(          Left parenthesis
)          Right parenthesis
,          Comma
.          Decimal point
$          Currency symbol
'          Apostrophe
:          Colon
!          Exclamation point
_          Underscore
"          Quotation mark

Lowercase alphabetic characters, the exclamation point (!), the underscore (_), and the double quote (") are extensions to Fortran 77. Digits are interpreted in base 10. A special character can serve as an operator, a part of a character constant, a part of a numeric constant, or some other function

Blank Characters
Use blank characters freely to improve the appearance and readability of Fortran statements. They have no significance in Fortran statements, except

• in character constants
• for H and character editing in format specifications
• in Hollerith constants
• to signify an initial line when used in column 6 of source line
• when counting the total number of characters allowed in any one Statement

These special considerations are discussed in detail in later sections.

Escape Sequences

Table lists escape sequences for representing non-graphic characters and for compatibility with the C programming language.

Table : C Escape Sequences

The compiler treats the backslash character as the beginning of an escape sequence by default. To use backslash as a normal character, compile the program with the –backslash option.