I just picked up Fortran yesterday at the suggestion of my mentor,
which for me means I glance through a tutorial and try to get a
program running that finds primes. I wrote this over the course of
maybe 15 minutes, debugged it as I was able to over the next 20, and I
don't think it is even close to compiling. Of course, I can't figure
out the exact issues with it, so any help would be appreciated.

program primes

integer :: i, j, k, l, m, n, x
real :: t
logical :: notprime, even

! Program finds primes up to
! upper limit 'x' as defined by user

write ( * , * ) 'Please input upper limit, x:'
read ( * , * ) x

Erg, never mind that the algorithm I wrote doesn't even work. Here is
the (hopefully) fixed version.

program primes

integer :: i, j, k, l, m, n, x
real :: t
logical :: notprime, even

! Program finds primes up to
! upper limit 'x' as defined by user

write ( * , * ) 'Please input upper limit, x:'
read ( * , * ) x

ALevenson wrote:

Why do you think there are "issues". If you've tried to compile it,
fix the things you understand and try to compile again. Repeat
until you don't understand it and then show us what happened.

ALevenson wrote:

It would help a lot if you would also indicate which specific errors
you're having trouble resolving.

ALevenson wrote:

...

I missed something the last time around, I don't know if it was part
that you changed or not.

In this form, you need to write:

t = i / REAL(m)

or,

t = REAL(i) / m

(One of the two has to be REAL to avoid doing integer division.)

My other comments stand.

Normally I do that, but I wanted to do some tests and see just how
fast Fortran can be compared to say, Perl.

I'm probably wrong, but if i is 3, wouldn't j = 1, while t = 1.5? It
was my way of testing to see if it was an even divisor, because I
wasn't sure if Fortran had an Int() function.

Also, I getting the errors:

primes.f90:38.33:

ALevenson wrote:

Where i = 3, 3 / 2 (integer division) = 1. Assigning to t then gives
you j = 1, t = 1.0.

ALevenson wrote:

Apart from what Dick says.....

So notprime is logical....

but later on you do

Don't do that. maybe
notprime = .true.
is what you want?

cheers,

paulv

Paul, I noticed that and fixed it AFTER I reposted,but didn't think
it'd be worth posting it a third time for that fix alone, i'd just
pollute the board.

Dick, how do I correct that, exactly? Do I condense it to a single
ampersand?
Also,if == does not work, how do I compare logicals?

Thanks for all your help so far.

ALevenson gmail.com> writes:

Hello,
seems it is time to get a manual.

AND is .AND. and NOT is .NOT.

It is quite long-winded and artificial, to say
prime .eqv. .true.
instead of
prime