In most BASICs, it in necessary to give each line of the program an identifying
line number in ascending sequence since lines are interpreted on an incremental
basis. FORTRAN differs since only certain statements are required to have
numbers and program execution does not depend upon a numerical sequence but on
the way in which statements are arranged – it starts at the first line and
finishes at the last! Statement numbers are usually only required. during loop
operations, data I/O of where control has to be passed to another part of the
There are occasions when text headings or complicated expressions or layouts are
used in a program where the space available for the statement (cols 7-72) is
insufficient. A continuation line (or lines) needs to be used to accommodate
the additional material; in such case, a character must be typed in column 6
and columns 1 – 5 left blank. Usually the first continuation line is labelled
With an ‘A’ the second with a ‘B” and so on; the figures 0 – 9 could also be
used if there are a lot of continuation Lines and F90 and ProFortran place no
restriction, unlike some Mainframes where a limit of 10 – 20 is quite common.
It is allowable, but not good practice to use the same symbol for succeeding
lines. The normal use of only 72 columns is a hangover from the days of
teletypes and was maintained when the majority of input was in the form of
It is perfectly possible to write small FORTRAN programs on the back of an
envelope before typing then into your micro – but a great deal easier if you use
a proper coding form for the purpose in which the various columns and fields are
shown; a typical example is shown in fig 1. A flow chart is useful when
constructing a new program, note that control characters which the text editor
may insect MUST BE REMOVED – the compiler tends to get uppity if it receives ^U
or ^G. The program must not be formatted in any way and I would not recommend
the use of DR’s ED which is only for the masochists – PEN, WordStar or HiSoft’s
ED are such better
The statement must start in or after column 7 of each Line, with a statement
label if needed in columns 1 – 5; the ‘tab’ facility could be used if one has a
dislike of using the space bar although this will usually start the statement in
column 9. If a continuation line is required, column 6 must be used as noted
earlier; program statements must finish in or before column 72 unless a
continuation line is to be used.
DATA NAMES AND TYPES
FORTRAN defines data specifically by name and, unlike most forms of BASIC, by
There are four names for data; constants (such as an explicitly stated numbers
or pieces of data); variables – which are symbolically identified pieces of
data; arrays which are ordered sets of data in 1,2 or 3 dimensions and array
elements which refer to one member of the set of data in an array.
Date types may be Integer, Real, Double Precision, Logical or Hollerith.
INTEGER types are precise representations of whole numbers, positive, negative
or zero in the range –32768 to +32767 and have a precision of 5 digits.
REAL types are approximations of real numbers, to 7+ significant digits which
may have a magnitude lying between 10^-38 and 10^38 (or 2^-127 and 2^127).