The diagram in Figure 1 shows
the major components of Fortran 90 [1],[2]. The size of each
slice of this ``pie" is roughly proportional to the number of
syntax rules needed to describe the features associated with
that slice, and hence is a measure of the structural
complexity of those features. (These measures should not,
however, be taken as an indication of conceptual or semantic
complexity nor of implementation effort-syntactic complexity
may or may not be related to these other forms of
complexity.)
- Fortran 77
- Fortran 90 is a super-set of
Fortran 77-all standard Fortran 77 programs are standard
Fortran 90 programs. Fortran 90 therefore encompasses and is
completely compatible with the existing Fortran 77
computational science infrastructure.
- Source Form
- To
Fortran 77's `fixed' source form Fortran 90 adds another
source form, called `free' source form, in which there are
no column dependencies. In free source form comments need
not start in column 1 and column 6 is not reserved for
continuation; continuation in free source form is indicated
by a trailing ampersand, on the `first' line. In both
source forms an exclamation point , `!', may be used to
initiate end-of-line comments (e.g., following a statement
on that line) and a semicolon may be used to separate two
statements on the same line. As in Fortran 77, Fortran 90
names (of variables, procedures, etc.) begin with a letter
and contain letters and digits; in addition, names may have
up to 31 characters, may contain underscore, `_',
characters, and may contain both upper and lower case
letters.
Figure 1: Fortran 90.
