program FindZeroNewton

implicit none
real:: f,f1
real::xc,xt,eps,xz
integer :: maxp,i
xt=-0.05
eps=.000000001
maxp=30

do i=1,maxp
   xc=xt-f(xt)/f1(xt)
   if(abs(xt-xc) < eps)exit 
   write(6,'(i2,3f11.6)')i,xc,xt,f(xt)
   xt=xc
enddo
if (i<=maxp)then
   xz=xc
   write(6,*)i,xz
else
   write(6,*)'nessuna soluzione in ',maxp,' passi'
endif

end program FindZeroNewton


real function f(x)
implicit none
real, intent(in)::x

f=x**2-1
end function f

real function f1(x)
implicit none
real, intent(in)::x

f1=2*x
end function f1