Re: Simple Program, Lots of Issues (F90)

ALevenson wrote:
> 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.

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.

> 
>       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
> 
>       do i = 2, x, 1
prime specific hint.
          write (*,*) 2
         do i = 3 , x, 2
If you do that, you won't have to worry about the evenness
stuff, just test the odd numbers starting at 3.


> ! Form of FOR loop is
> ! do variable = start val, end val, step size
>          if ( i == 2 ) then
>             write ( * , * ) i
>          end if
>          even = .FALSE.
>          notprime = .FALSE.
>          j = i / 2
>          t = i / 2
>          if ( j == t ) then
Why would you ever expect j and t to be different?  Division
is usually repeatable on most machines ;) .
>             even = 1
>          else
>             l = SQRT( i )
The Fortran SQRT function requires a real argument, not an
integer.  Try SQRT(REAL(I)), although there is a better
way that doesn't need a SQRT
>             do m = 3, l, 2
>                n = m / 2
>                t = m / 2
>                if ( n == t ) then
Ditto for n and t
>                   notprime = 1
>                end if
>             end do
>          end if
>          if ( notprime == .FALSE. && even == .FALSE. ) then
>             write ( * , * ) i
>          end if
>       end do
> 
>       stop
>       end