PROGRAM - main program
FUNCTION - function, FUNCTION can be preceded
by some of the specifications of the
variables below, except IMPLICIT
SUBROUTINE - subroutine
??ENTRY - extra entry in subprograms
? BLOCK DATA - common data, usually given initial values
IMPLICIT - default IMPLICIT REAL(A-H, O-Z), INTEGER(I-N)
IMPLICIT NONE - not standard, but very useful, it is available
in Fortran 90. Gives the "Pascal convention"
that all variables have to be specified. For
Sun and DEC the same effect can be obtained
with the switch -u in the compilation command
INTEGER
REAL
DOUBLE PRECISION
COMPLEX
LOGICAL
CHARACTER CHARACTER*4
DIMENSION - can also be given directly in the type specification,
as well as in a COMMON
? COMMON - common storage area for variables that are
in several program units
??EQUIVALENCE - common storage area for several variables in the
same program unit
PARAMETER - makes a variable into a constant with a certain value
EXTERNAL - tells the system that the identifier is an
external function or an external subroutine
INTRINSIC - tells the system that the identifier is an
intrinsic function (or a subroutine, only in
Fortran 90)
SAVE - saves the values between exit or return from one
subroutine into the new call of the same
subroutine or function
DATA - puts initial values into variables
GOTO snr1 - ordinary GOTO statement (jumps to the statement with
number snr1)
? GOTO (snr1, snr2, snr3), integer_expression
- conditional GOTO statement. If the integer
expression is 1, 2 or 3, execution jumps to
statement number snr1, snr2 or snr3 (an arbitrary
number of statement numbers snr are permitted).
??GOTO statement_number_variable, (snr1, snr2, snr3)
- an assigned GOTO statement, jumps to the statement
number that equals the statement
number variable (an arbitrary number of
statement numbers snr are permitted).
??GOTO statement_number_variable
- this is an assigned ordinary GOTO statement, it is a
combination of the first one, GOTO snr1, and
previous one, GOTO statement_number_variable without
a list of permitted alternatives.
??ASSIGN statement_number TO statement_number_variable
- statement number variables can not be assigned with
an ordinary assignment of the type (integer
variable = integer expression), it has to be
done with the ASSIGN statement. The statement
number variable can then be used for an assigned
GOTO statement and in the ordinary GOTO statement
and also in connection with FORMAT.
? IF (numerical_expression) snr1, snr2, snr3
- arithmetical IF-statement, jumps to statement number
snr1 if the expression is negative,
snr2 if the expression is zero,
snr3 if the expression is positive
IF(logical_expression) statement
- conditional statement: if the logical expression
is true, the statement is performed, in the
other case execution jumps directly to the next
statement. The statement here is permitted to
be an ordinary assignment statement or an
ordinary jump statement (GOTO statement) or a
call of a subroutine.
IF(logical_expression) THEN ! Complete alternative statement.
...statements... ! Variants without the ELSE-part as well
ELSE ! as with nested ELSE, or with
...statements... ! ELSE replaced by
ENDIF ! ELSE IF (log_expr) THEN
! also exist.
CONTINUE - continuation, does nothing. It is recommended for
clean conclusion of a DO-loop.
STOP - concluding statement, stops execution.
END - concluding statement, stops compilation of the
program unit and also execution if it is
in the main program.
If END is found during execution of a subprogram,
an automatic return to the calling program unit
is executed (replaces the explicit RETURN statement).
? PAUSE - pause statement, stops execution temporarily
(implementation dependent).
DO statement_number variable = var1, var2, var3
- DO-loop.
Floating-point numbers are permitted as variables
in the DO-loop, but they are not recommended.
It is preferable to use integers.
OPEN - open a file before the program can use it.
CLOSE - close a file. A file that has not been closed can
usually not be read.
READ - input
WRITE - output
PRINT - previously output to line printer, now a synonym to
WRITE. It works on a standard unit.
INQUIRE - inquires about file status.
REWIND - rewinds a file to the beginning.
BACKSPACE - rewinds a file one record.
ENDFILE - marks end of file.
FORMAT - Fortran speciality (see below).
CALL sbrtn - call a subroutine sbrtn.
fnctn - a function is called by giving the function
name fnctn.
RETURN - return from the subprogram (subroutine or
function).
Example Comments
-------------------------------------------------------------------
Integer I I5 5 positions reserved
-------------------------------------------------------------------
Floating-point F F8.3 8 positions, out of which 3 are
number used for the fractional part
E E14.6 14 positions of which
6 are used for the decimals
4 - for the exponent
1 - for the sign
1 - for the starting zero
1 - for the decimal point
1 - for a blank character
D D20.12 as E, but for double precision
G G14.6 as F, if the number can be given
within the field, else as E
-------------------------------------------------------------------
Complex numbers as a pair of floating-point variables
-------------------------------------------------------------------
Logical L L1
Character A A7 7 characters are available in A7
string
' ' 'Example' Conventional character constant
nH 7HExample Hollerith constant (obsolete)
Positioning Tn n positions from the left
TLn n positions towards left
TRn n positions towards right
nX n positions towards right
Last new line $ this is used if you wish to
do input in direct connection
with an output, to stay on
the same line. Not standard!
Not Fortran 90!
Discontinue : if the list does not contain
any more elements the
format is also finished here
New record / normally a new line
-------------------------------------------------------------------
Binary B not Fortran 77 but Fortran 90
Octal O not Fortran 77 but Fortran 90
Hexadecimal Z not Fortran 77 but Fortran 90
-------------------------------------------------------------------
Output SP + is written
SS + is not written
S standard (normal SS)
In all alternatives a minus - is written for negative values
-------------------------------------------------------------------
Input BZ blanks are interpreted as
zeroes
BN blanks are not regarded as
anything (blanks are skipped)
BN is standard using the ULTRIX, when punched cards were used,
BZ was the standard. Compare with BLANK = "ZERO" and
Blank = "NULL" in the OPEN-statement.
-------------------------------------------------------------------
Scaling factor kP:
Input: with an exponent, no action.
Without exponent, the number
is multiplied by 10**(-k)
before assignment, which means
a change of the value.
Output: with exponent, the mantissa
is multiplied by 10**k and the
exponent is reduced with k,
which means no change of the
value.
Without exponent, the
number is multiplied by 10**k
before the output, which means
a change of value.
NB! S, SP, SS, BN, BZ and kP are valid until the
end of the FORMAT or
until a new one of the same kind appears. To scale with kP
is good with E-format on output, because then you avoid that the first
digit is zero, and you get more information into less space on
the paper. To scale with kP is catastrophic using F-format, but
it was of great interest when punched cards were still in use.
A very good and complete description of input and output in Fortran, including the use of the FORMAT-letters, is given in the book by Adams et al (1992).
fpr < output_file | lpr -Pprinterwhere output_file is the name of the file to be printed with control characters and printer is the name of the printer to be used.