New to Fortran (just started today), having trouble with the natural logarithm:
PROGRAM log
IMPLICIT NONE
REAL :: x
PRINT *, "Enter a number:"
READ *, x
x = log (x)
PRINT *, "The natural log of x is:", x
END PROGRAM log
The compiler keeps throwing up the error:
x = log (x)
1
Error: Symbol at (1) is not appropriate for an expression
Other intrinsic functions work fine. What am I doing wrong?
The problem is that you've shadowed (overridden) the definition of the symbol log - which would normally refer to the standard library mathematical function - with the name of your program, which is also log. If you change the name of the program to, say, logtest:
PROGRAM logtest
...
END PROGRAM logtest
You'll find that the program works as expected.
Related
I'm very new at Fortran. I'm trying to compile this Fortran, I think 90??? Code. I'm using visual studio with the intel compiler.
The following code is giving me an error 5082. I have absolutely no idea why. Like literally no clue. Please, please help.
integer function Dub(n)
integer n
Dub = 2*n
return
end
program Subroutines
implicit none
! Variables
integer n
n = 5
! Body of Subroutines
write(*,*) n
Dub(n)
write(*,*) 'Press Enter to Exit'
read(*,*)
stop
end program Subroutines
In Fortran a call to a function, or a subroutine, must be part of a statement (or an initialization expression, but that's more advanced). name(argument[s]) by itself is not a statement, unlike some other languages such as C, C++ and Java. A function call must be in an expression, and a subroutine call must use the call keyword. See https://en.wikibooks.org/wiki/Fortran/Fortran_procedures_and_functions for examples.
Changing that line of your program to n = Dub(n) would make it legal, but rather useless. That function does nothing except return a value, and your main program does nothing useful with the value returned. Generally you call a function because you want either a side effect from executing the function, or to use the returned value, or both.
I am writing the following simple routine:
program scratch
character*4 :: word
word = 'hell'
print *, concat(word)
end program scratch
function concat(x)
character*(*) x
concat = x // 'plus stuff'
end function concat
The program should be taking the string 'hell' and concatenating to it the string 'plus stuff'. I would like the function to be able to take in any length string (I am planning to use the word 'heaven' as well) and concatenate to it the string 'plus stuff'.
Currently, when I run this on Visual Studio 2012 I get the following error:
Error 1 error #6303: The assignment operation or the binary
expression operation is invalid for the data types of the two
operands. D:\aboufira\Desktop\TEMP\Visual
Studio\test\logicalfunction\scratch.f90 9
This error is for the following line:
concat = x // 'plus stuff'
It is not apparent to me why the two operands are not compatible. I have set them both to be strings. Why will they not concatenate?
High Performance Mark's comment tells you about why the compiler complains: implicit typing.
The result of the function concat is implicitly typed because you haven't declared its type otherwise. Although x // 'plus stuff' is the correct way to concatenate character variables, you're attempting to assign that new character object to a (implictly) real function result.
Which leads to the question: "just how do I declare the function result to be a character?". Answer: much as you would any other character variable:
character(len=length) concat
[note that I use character(len=...) rather than character*.... I'll come on to exactly why later, but I'll also point out that the form character*4 is obsolete according to current Fortran, and may eventually be deleted entirely.]
The tricky part is: what is the length it should be declared as?
When declaring the length of a character function result which we don't know ahead of time there are two1 approaches:
an automatic character object;
a deferred length character object.
In the case of this function, we know that the length of the result is 10 longer than the input. We can declare
character(len=LEN(x)+10) concat
To do this we cannot use the form character*(LEN(x)+10).
In a more general case, deferred length:
character(len=:), allocatable :: concat ! Deferred length, will be defined on allocation
where later
concat = x//'plus stuff' ! Using automatic allocation on intrinsic assignment
Using these forms adds the requirement that the function concat has an explicit interface in the main program. You'll find much about that in other questions and resources. Providing an explicit interface will also remove the problem that, in the main program, concat also implicitly has a real result.
To stress:
program
implicit none
character(len=[something]) concat
print *, concat('hell')
end program
will not work for concat having result of the "length unknown at compile time" forms. Ideally the function will be an internal one, or one accessed from a module.
1 There is a third: assumed length function result. Anyone who wants to know about this could read this separate question. Everyone else should pretend this doesn't exist. Just like the writers of the Fortran standard.
I was trying to test my cryptography algorithm by [diehard tests] (http://stat.fsu.edu/pub/diehard/), that I realized my input file must be an unformatted and direct access file.
So I tried to write a simple program in Fortran to read from a file and write it to another.
First of all, is it the only way to make an unformatted or direct access file ?
If it is so, I've got this Error
open(unit=2, file='unf.BIN',RECL=rl , form='UNFORMATTED', access='direct')
1
Error: Syntax error in OPEN statement at (1)
I use RECL because of some missing RECL parameter in Open statement errors.(Fortran 90, Compiling program: Error messages)
Here is my Fortran code:
program BinaryWriter
implicit none
integer :: i
integer :: p
open(unit=1,file='encout')
open(unit=2, file='unf.BIN',RECL=rl , form='UNFORMATTED', access='direct')
do i=1 ,256
read (8,'(i1)') p
write(*,*) p
end do
close(1)
close(2)
end program BinaryWriter
Two things:
1) Please stop using unit numbers less than 10. Virtually all modern Fortran compilers do now have the newunit identifier, which, instead of the old unit actually picks an unused value, so always use a variable there. But even if you want to use unit, set it to a value of 10 or more.
2) For direct access, the program needs the record length. So if you have access="direct", you also need an recl=<some integer value> to tell the compiler where a new record starts.
Now in your case, you have a RECL=rl entry in the open statement, but I can't see what rl is. It needs to be a positive integer.
Edit to add: As #IanH pointed out in a comment below your question, it is possible that you are using fixed form fortran. This might be caused by the file extension of your source code file being .f or .f77. In that case, you'd have to wrap your lines manually:
program dir
implicit none
integer :: rl
open(unit=20, file='delme.bin', recl=<the record length>,
& form='unformatted', access='direct')
close(20)
end program dir
Note that the & is in the 6th position of the line. Fortran 77 code usually uses a + there, but & is also compatible with newer Fortran versions, that's why I prefer it. F77 standard is just any character in that 6th spot.
I'm having a runtime error when I run a code that works without problems using a different computer.
I'm wondering if the problem is the Fortran compiler of this machine (GCC 4.9.2) since the former computer used a previous version.
The issue comes when defining a variable like this:
In a module I define
character(30),allocatable,save :: sceneclass(:)
Then in the subroutine sceneclass is defined according to
character(30) surf, frac, scene
allocate(sceneclass(10))
do i=1,10
write(sceneclass(i),*) trim(scene)//trim(surf)//'_'//trim(frac)
enddo
In the first iteration I get the "End of record". But I don't know where is the problem. It seems to work fine in other computers.
You are probably writing a string to sceneclass(i) that is longer then the 30 chars you specified.
I can reproduce this with
program test
implicit none
character(10),allocatable :: sceneclass(:)
integer :: i
allocate( sceneclass(10) )
do i=1,10
write(sceneclass(i),*) 10**i
enddo
print *, ( trim(sceneclass(i)), i=1,10 )
end program
gfortran fails with
Fortran runtime error: End of record
while ifort reports the error correctly:
output statement overflows record, unit -5, file Internal List-Directed Write
Increasing the string length to 12 solves the issue in this case. You can (and should) use iostat within the write statement to capture this.
One thing to be aware of, when you specify a list directed * write of a character string, the compiler always(?) adds an extra lead blank, so the effective length of the string you can write is one less than you might expect.
To remedy that (and of course assuming you don't want the lead blank anyway ) use a string edit descriptor:
write(sceneclass(i),'(a)')...
Interestingly ifort (linux 11.1) actually allows you to overrun by one character:
character*5 c
write(c,*)'12345' ! result: " 1234"
which I would consider a bug. It seems they forgot to count the blank too.. ( gfortran throws the above error on this, and ifort balks if you add one more character )
see here if you wonder why the blank.. Are Fortran control characters (carriage control) still implemented in compilers?
and now I'm curious if some compiler somewhere didn't do that for an internal list write, or maybe your code was previously compiled with a flag to disable the "printer control" code
I'm learning Fortran for a new job and started writing some very, very basic programs. To compile, I'm using gcc version 4.6.2, and I'm working on Linux Suse OS (if that matters at all). I believe the version of Fortran I'm using is F90 or F95. The code is written using the VIM text editor.
Here is the program I've written
INTEGER, PARAMETER :: x = 2, y = 3
INTEGER :: z = x+y
print *, z
That's it! Oh, and the lines are indented, They start on column 8, so indentation isn't an issue.
UPDATE 1
I have tried doing this like so:
PROGRAM print_stuff
print *, z
END PROGRAM print_stuff
I also tried adding the IMPLICIT NONE statement to all of that and didn't get a change in the error.
END UPDATE 1
I save, quit, and compile. The compiler returns this error:
Error: Unexpected end of file in 'practice1.f'
Anyone know what the problem is? I've even tried removing the print statement and just having the variable declarations but the same error occurs. It's keeping me from practicing Fortran at all!
Your first version
INTEGER, PARAMETER :: x = 2, y = 3
INTEGER :: z = x+y
print *, z
is NOT a valid Fortran program. Every valid program ends with the end statement. A 'program' without an end statement is not syntactically correct. Keep reading your introductory tutorial.
I suggest you get into the habit of starting your programs with a program statement, with a name, such as
program myprog
and ending them with
end program myprog
Strictly, neither the program statement nor a program name is necessary but they do make things look a bit more comprehensible.
Oh, and while I'm writing ... don't get into the habit of starting lines at column 8, that smacks of the now out-dated fixed-form source. If you are using a reasonable compiler (such as gcc) give your filenames the .f90 suffix and let your source code run free. All the while observing good habits of indentation of course.
EDIT in response to OP's edits
PROGRAM print_stuff
print *, z
END PROGRAM print_stuff
and
INTEGER, PARAMETER :: x = 2, y = 3
INTEGER :: z = x+y
print *, z
END
are both syntactically correct. Both gfortran (v4.1.2) and Intel Fortran (v13.0.1) compile both correctly and produce executables which execute.