Fortran Programming Language :: problem reading REALs from *


	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+((b2)-(4ac))*0.5)/(2a) Thanks, JB "J" <nospamplease> wrote in message news:6a-dnUAxt7LSzKDbnZ2dnUVZ_rKvnZ2d@adelphia.com... - Hide quoted text - > 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+((b2)-(4ac))*0.5)/(2a) 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)-(4ac))0.5)/(2a) ... >You need 3 reals for the quadratic formula, which looks to be coded >correctly. It compiles but still needs some work. ((b*2)-4ac))0.5 is not wrong but sqrt((b2)-4ac) 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... - Hide quoted text - > 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+((b2)-(4ac))*0.5)/(2a) > Thanks, > JB 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