Integer overflow

Hi all ,
I have written program below which occurs integer overflow in factorial operation for n > 31

How can i handle this?


A quick google search says that the maximum 32bit integer value is 2,147,483,647.
So you can’t calculate any values larger than this without increasing the size of the integer you’re using.
I expect that your program is not giving correct answers for factorials above 12!

One option for a larger integer, is to use the int64 kind from the iso_fortran_env module:

program main
  use iso_fortran_env, only: int64
  implicit none
  integer(int64) :: n, i, s_1, s_2, s_3, factorial
end program main

According to google, max value for 64bit int is 9,223,372,036,854,775,807.
If you don’t need the precision, you could also just use a float-point (real) variable for your factorial result.

edit: to use iso_fortran_env instead

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Thank you very much :pray:

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The intrinsic huge returns the maximum value in a given variable type.

print *, huge(factorial)

prints the maximum value that can be stored in a default integer variable as factorial.


if you come from Python, you can be disappointed because in Python you can use arbitrarily long integers:

>>> 44568668*345346344747*57457455585*353523463473474585*66347474735583

But in Fortran, you will need a specific library to do such things (there is surely one, but don’t ask me…)
Fortran uses the hardware to compute fast. Python can go beyond but at the expense of the speed.