Declarations and Types

Types

INTEGER

for exact whole numbers;

REAL and COMPLEX

for approximate, fractional numbers; for the latter a pair of REAL numbers are used;

CHARACTER

for strings of one or more characters;

LOGICAL

for objects which may have the values TRUE and FALSE, only.

DOUBLE PRECISION

Redundant and obsolete!

Variables

Examples:

INTEGER :: count, number_of_students REAL :: price, root_1, root_2 count = 42 root_1 = 3.141 root_2 = 1.77E-2 CHARACTER :: answer CHARACTER(LEN=10) :: name answer = 'Y' name = 'Backus' LOGICAL :: Spock, Kirk Spock = .TRUE. Kirk = .FALSE.

Implicit Declaration, IMPLICIT NONE

• The Standard does not require that integers and reals be declared. If not declared:
  • those beginning with I -- N assumed INTEGERs;
  • others assumed REAL;
  
  
• Declare all your variables!

  PROGRAM declarations IMPLICIT NONE ! -- The first line in any programme unit!! CHARACTER(LEN=20) :: name REAL, PARAMETER :: pi = 3.14159265 END PROGRAM declarations

Case INsensitive

• Fortran is case INsensitive --- the only(?) language in common use;
  
  
• Contrast F...