Begginer fortraner: stuck on arithmatic

[Molymoles]

Hi All.
I am trying to rewrite a program that i have in matlab to one in fortran. as i chug along, i am comparing the results and i am getting funny answers. This is the program in have in fortran so far:

ccccccccccccccccccccccccccccccccccccccccccccccccc
program main
implicit none
ccccccccccccccccccccccccccccccccccccccccccccccccc
integer Nstep, Xstep
double precision x, t, dt, dx
double precision K1, K2, Vmax, KM, P, Po
double precision Co, Qo, Cop,DeltaQ
double precision A1, A2, A3
cccccccccccccccccccccccccccccccccccccccccccccccccc
t = 1.0d0
x = 0.5d0
Xstep=2**8
dx=1/Xstep
dt=0.0005d0
Nstep=t/dt
Co = 275.0d-6
Vmax = 14.50d-9
cccccccccccccccccccccccccccccccccccccccccccccccccc ccccccccccccccccc
print *, "t, x,Nstep, Xstep dx,dt",t,x,Nstep, Xstep,dx,dt
print*, "Co, Vmax", Co, Vmax
cccccccccccccccccccccccccccccccccccccccccccccccccc
return
end

the results i get when i run it with f77 f1.f (f1.f is what i called the file) is this:
t, x,Nstep, Xstep dx,dt 1. 0.5 1999 256 0. 0.0005
Co, Vmax 0.000275 1.45E-08

with the first line i have major problmes: Nstep=1/.0005 and should be 2000, why is it 1999 ............and dx=1/Xstep=0 but it should be equal to .0039

why am i getting such funny results?

 

[mikrom]

Read about the Mixed Type Arithmetic here

http://www.math.hawaii.edu/lab/197/fortran/fort3.htm

 

[mikrom]

Now I am on computer which has g77 compiler
So here is your corrected example

program main
implicit none
integer Nstep, Xstep
double precision x, t, dt, dx, Nstep_Double
double precision K1, K2, Vmax, KM, P, Po
double precision Co, Qo, Cop,DeltaQ
double precision A1, A2, A3
t = 1.0d0
x = 0.5d0
Xstep=2**8
! 1. says the compiler that result should by double,
! otherwise the result will be Integer, because 1 and Xstep are Integers.
dx=1./Xstep
dt=0.0005d0
! Compute result with Double Datatypes
Nstep_Double=t/dt
! Store result to Integer
Nstep = Nstep_Double 
Co = 275.0d-6
Vmax = 14.50d-9
print *, "t, x,Nstep, Xstep dx,dt",t,x,Nstep, Xstep,dx,dt
print*, "Co, Vmax", Co, Vmax
return
end

 

[Molymoles]

Works beautifully, your help is most appreciated.

 

[mikrom]

Then gimme the Star