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problem reading REALs from *


real a,b,c
write(*,10)
10 format('enter a: ',/)
read(*.*)a
write(*.15)a
15 format('a is ',F5.7)

I think the output of writing a as F5.7 is bad - that means width 5 with 7
decimals precision....impossible, but that shouldn't cause the x1 output to
be nan.

I'm helping a poor girl finish her last semester in college from her
hospital bed, and I have experience in C/java and visual basic.  I figured
we'd do a practice program that simply read a, b, and c from standard input
and calculated x1 and x2 from the quadratic formula.  Problem is, all I ever
get is nan (not a number) from the calculations, and the test writes of a,
b, and c immediately after they're 'read' are all *****.  What am I missing?

I understand there are different fortran syntaxes available, but from the
class projects so far, this is the style they use.

also,

x1= (-b+((b**2)-(4*a*c))**0.5)/(2*a)

Thanks,
JB

"J" <nospamplease> wrote in message

news:6a-dnUAxt7LSzKDbnZ2dnUVZ_rKvnZ2d@adelphia.com...

You needed commas where you had periods.
real a
write(*,10)
10 format('enter a: ')
read(*,*)a
write(*,15)a
15 format('a is ',F10.5)
end
You need 3 reals for the quadratic formula, which looks to be coded
correctly.  It compiles but still needs some work.  What if the discriminant
is less than zero?
--
ww
On May 5, 10:53 pm, "J" <nospamplease> wrote:

> real a,b,c
> write(*,10)
> 10 format('enter a: ',/)
> read(*.*)a
> write(*.15)a
> 15 format('a is ',F5.7)

A beginner should not fuss with FORMAT statements. The program below
shows how to read and then display a real variable.

real a
write(*,*) "enter a"
read (*,*) a
write (*,*) "a =",a
end

In article <4LCdnX8nEM5wxKDbnZ2dneKdnZydn@comcast.com>,

Wade Ward <inva@invalid.nyet> wrote:

>"J" <nospamplease> wrote in message
>news:6a-dnUAxt7LSzKDbnZ2dnUVZ_rKvnZ2d@adelphia.com...

>> x1= (-b+((b**2)-(4*a*c))**0.5)/(2*a)
...
>You need 3 reals for the quadratic formula, which looks to be coded
>correctly.  It compiles but still needs some work.

((b**2)-4*a*c))**0.5 is not wrong but sqrt((b**2)-4*a*c) should run
faster. There are many ways to get substandard answewrs from that
formula, though, beautifully explained by George E. Forsythe, "Solving
a Quadratic Equation on a Computer, in "The Mathematical Sciences:
Essays for COSRIMS" p.138-152 (MIT Press 1969)

-- John Harper, School of Mathematics, Statistics and Computer Science,
Victoria University, PO Box 600, Wellington 6140, New Zealand
e-mail john.har@vuw.ac.nz phone (+64)(4)463 5341 fax (+64)(4)463 5045

"J" <nospamplease> wrote in message

news:6a-dnUAxt7LSzKDbnZ2dnUVZ_rKvnZ2d@adelphia.com...

I want to thank you all for your input.  I believe i had 2 problems masking
each other - the formatting made me think I wasn't reading floats properly
(how do you fit 7 decimals of precision in only 5 spaces?) and the numbers I
was using to test the formula were bogus so of course i came up with 'nan'.
It seems my program was fine.  Just stupid mistakes.

JB

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