# Floating point exception

**URL:** <https://fortran-lang.discourse.group/t/floating-point-exception/4610>\
**Category:** Help\
**Created:** [October 24, 2022, 7:11pm UTC](https://fortran-lang.discourse.group/t/floating-point-exception/4610 "2022-10-24T19:11:07Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![yeti0904](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/yeti0904/32/1886_2.png) [@yeti0904](https://fortran-lang.discourse.group/u/yeti0904)\
**Post date:** [October 24, 2022, 7:11pm UTC](https://fortran-lang.discourse.group/t/floating-point-exception/4610/1 "2022-10-24T19:11:07Z")

</div>

```auto
module Util
    use, intrinsic :: iso_c_binding, only : c_int
    interface
        function Util_Rand() bind(c, name = "rand")
            import c_int
            integer(c_int) :: Util_Rand
        end function Util_Rand
        subroutine Util_SeedRand(seed) bind(c, name = "srand")
            import c_int
            integer(c_int) :: seed
        end subroutine Util_SeedRand
    end interface
    contains
    function Util_RandomRange(minimum, maximum)
        integer :: Util_RandomRange
        integer :: minimum, maximum
        integer :: randReturn

        randReturn = Util_Rand()
        Util_RandomRange = mod(randReturn + minimum, maximum)
    end function Util_RandomRange
end module Util

```

at line 20:

```auto
Util_RandomRange = mod(randReturn + minimum, maximum)

```

there is a floating point exception error

```auto
Program received signal SIGFPE: Floating-point exception - erroneous arithmetic operation.

Backtrace for this error:
#0 0x7ffaa6e519ff in ???
#1 0x55a77658b530 in __util_MOD_util_randomrange
        at src/util.f90:20
#2 0x55a77658b9e7 in __minefield_MOD_minefield_init
        at src/minefield.f90:32
#3 0x55a77658bee7 in ygms
        at src/main.f90:14
#4 0x55a77658bf6e in main
        at src/main.f90:3

```

---

<div class="post-metadata">

**Author:** ![PierU](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/pieru/32/1848_2.png) [@PierU](https://fortran-lang.discourse.group/u/PierU)\
**Post date:** [October 24, 2022, 7:53pm UTC](https://fortran-lang.discourse.group/t/floating-point-exception/4610/2 "2022-10-24T19:53:57Z")

</div>

Hello,

Could you give a minimal reproducible example (.i.e. the smallest possible piece of code that can be compiled and run) where it fails? And which command line you used to compile?

I compiled it with gfortran and just repeatedly call `Util_RandomRange()` with random integers, and couldn’t see a single error. And a floating point error in a code that involves only integers looks quite strange.

---

<div class="post-metadata">

**Author:** ![yeti0904](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/yeti0904/32/1886_2.png) [@yeti0904](https://fortran-lang.discourse.group/u/yeti0904)\
**Post date:** [October 24, 2022, 8:33pm UTC](https://fortran-lang.discourse.group/t/floating-point-exception/4610/3 "2022-10-24T20:33:28Z")

</div>

```auto
module Minefield
    ! modules
    use :: Util
    use, intrinsic :: iso_c_binding

    ! types
    implicit none
    type :: Vec2_t
        integer :: x, y
    end type
    type :: Minefield_Tile_t
        logical :: mine
        integer :: around
        logical :: covered
    end type 

    ! variables
    type(Minefield_Tile_t), dimension(:, :), allocatable :: Minefield_array
    type(Vec2_t) :: Minefield_boardSize

    ! functions
    contains
    subroutine Minefield_Init()
        integer :: i, j ! iterator
        integer :: number
        integer :: mineX
        integer :: mineY

        allocate(Minefield_array(Minefield_boardSize%y, Minefield_boardSize%x))

        ! randomly place mines
        do i = 0, 10
            mineX = Util_RandomRange(1, Minefield_boardSize%x)
            mineY = Util_RandomRange(1, Minefield_boardSize%y)

            Minefield_array(mineX, mineY)%mine = .true.
        end do

        ! calculate numbers
        do i = 1, Minefield_boardSize%x
            do j = 1, Minefield_boardSize%y
                number = 0
                Minefield_array(i, j)%around = 0
                Minefield_array(i, j)%covered = .true.
                if (.not. Minefield_array(i, j)%mine) then
                    if ((i > 1) .and. (Minefield_array(i - 1, j)%mine)) then
                        number = number + 1
                    end if
                    if ((i < Minefield_boardSize%x) .and. (Minefield_array(i + 1, j)%mine)) then
                        number = number + 1
                    end if
                    if ((j > 1) .and. (Minefield_array(i, j - 1)%mine)) then
                        number = number + 1
                    end if
                    if ((j < Minefield_boardSize%y) .and. (Minefield_array(i, j + 1)%mine)) then
                        number = number + 1
                    end if
                    ! diagonal
                    if ( &
                        (i > 1) .and. (j > 1) .and. &
                        (Minefield_array(i - 1, j - 1)%mine) &
                    ) then
                        number = number + 1
                    end if
                    if ( &
                        (i > 1) .and. (j < Minefield_boardSize%y) .and. &
                        (Minefield_array(i - 1, j + 1)%mine) &
                    ) then
                        number = number + 1
                    end if
                    if ( &
                        (i < Minefield_boardSize%x) .and. (j > 1) .and. &
                        (Minefield_array(i + 1, j - 1)%mine) &
                    ) then
                        number = number + 1
                    end if
                    if ( &
                        (i < Minefield_boardSize%x) .and. (j < Minefield_boardSize%y) .and. &
                        (Minefield_array(i + 1, j + 1)%mine) &
                    ) then
                        number = number + 1
                    end if
                end if

                Minefield_array(i, j)%around = 0
            end do
        end do
    end subroutine Minefield_Init
end module Minefield

```

this is the module that contains the function that calls `Util_RandomRange`, so to run it i guess you just do

```auto
program main
    using :: Minefield
    call Minefield_Init
end program main

```

---

<div class="post-metadata">

**Author:** ![PierU](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/pieru/32/1848_2.png) [@PierU](https://fortran-lang.discourse.group/u/PierU)\
**Post date:** [October 24, 2022, 8:58pm UTC](https://fortran-lang.discourse.group/t/floating-point-exception/4610/4 "2022-10-24T20:58:57Z")

</div>

In `Minefield_Init()` , `Minefield_boardSize` is not initialized before you use it. Ultimately you are doing `mod(0,0)`, which is illegal.

---

<div class="post-metadata">

**Author:** ![yeti0904](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/yeti0904/32/1886_2.png) [@yeti0904](https://fortran-lang.discourse.group/u/yeti0904)\
**Post date:** [October 24, 2022, 9:28pm UTC](https://fortran-lang.discourse.group/t/floating-point-exception/4610/5 "2022-10-24T21:28:37Z")

</div>

thanks, it doesn’t crash now