fortran averaging columns frame by frame in specific format - fortran

Question

I would like to average first column and last column shown here(that is my output). My code does several things such as compare specific atoms with the name "CA" for each frame (I have 1000 frames), exclude the nearest neighbours and depending on the cutoff value, and count those contacts and print them separately according to my wish (input file looks like this). I would like to print a file where it gives me the output something like following as an example:
1 0
2 12
3 12
....
100 16
Need guidance to achieve that by helping me form a loop or a condition.
open(unit=11,file="0-1000.gro", status="old", action="read")
do f=1,frames,10
25 format (F10.5,F10.5,F10.5)
do h=1,natoms_frames
read(11,format11)nom(h),resname(h),atmtype(h),num(h),x(h),y(h),z(h)
end do
read(11,25)lasta(f),lastb(f),lastc(f)
count=0
do h=1, natoms_frames
if (atmtype(h).eq.' CA') then
count=count+1
CAx(count)=x(h)
CAy(count)=y(h)
CAz(count)=z(h)
end if
end do
do h=1, count
avg_cal=0
cal=0
do hh=h+3, count
if (h.ne.hh) then
! finding distance formula from the gro file
distance = sqrt((CAx(hh)-CAx(h))**2 + (CAy(hh)-CAy(h))**2 + (CAz(hh)-CAz(h))**2)
if (distance.le.cutoff) then
cal = cal+1
set = set+1
final_set=final_set+1
avg_cal=avg_cal+1
end if
end if
end do
write(*,*)h,cal,final_set
end do
end do ! end of frames
close(11)
end program num_contacts

Answer 1

Writing in a file (in ASCII) is the same as printing on screen, except that you need to specify the file's unit.
So first, open your file:
open(unit = 10, file = "filename.dat", access = "sequential", form = "formatted", status = "new", iostat = ierr)
where 'unit' is a unique integer that will be associated to your file (as an ID). Note that the 'form' is 'formatted' as you want to output something readable by a human. Then you can start your loop:
do h = 1, natoms_frames
! BUNCH OF STUFF TO CALCULATE REQUIRED VARIABLES
write(10, *) h, cal, final_set
end do
Finally, close your file:
close(10)