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module factorial_demo
public :: factorial
logical, save, public :: debug = .false.
contains
recursive function factorial (n) result (r)
integer, intent (in) :: n
integer :: r
if ( debug ) then
print *, "Entering factorial with n = ", n
end if
select case (n)
case (:-1)
print *, "Bad value for n ", n
stop
case (0, 1)
r = 1
case (2:)
r = n*factorial(n-1)
end select
if (debug) then
print *, "Leaving factorial for n= ", n, ", n! = ", r
end if
end function factorial
end module factorial_demo
program try_fact
use factorial_demo
integer :: n, v
character(len=1) :: d
outer: do
print *, "Enter a number"
read *, n
print *, "Do you want to debug?"
do ! Look for Yes, No, or Quit
read *, d
select case (d)
case ("Y", "y")
debug = .true.
exit
case ("N", "n")
debug = .false.
exit
case ("Q", "q")
exit outer
case default
print *, "Enter `yes', `no' or `quit'!"
end select
end do
v = factorial(n)
print "(i5, a, i15)", n, "! = ", v
end do outer
end program try_fact
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