# Allocatable array defined or not

**URL:** <https://fortran-lang.discourse.group/t/allocatable-array-defined-or-not/3736>\
**Category:** Help\
**Created:** [June 12, 2022, 6:13pm UTC](https://fortran-lang.discourse.group/t/allocatable-array-defined-or-not/3736 "2022-06-12T18:13:14Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![fortran4r](https://avatars.discourse-cdn.com/v4/letter/f/9de0a6/32.png) [@fortran4r](https://fortran-lang.discourse.group/u/fortran4r)\
**Post date:** [June 12, 2022, 6:13pm UTC](https://fortran-lang.discourse.group/t/allocatable-array-defined-or-not/3736/1 "2022-06-12T18:13:14Z")

</div>

```auto
program test
  use ieee_arithmetic, only: ieee_value, ieee_quiet_nan
  real(8) :: x1(5)
  real(8), allocatable :: x2(:)
  allocate(x2(5))
  x1(1) = ieee_value(0d0, ieee_quiet_nan)
  x2(1) = ieee_value(0d0, ieee_quiet_nan)
  print *, x1(2:5)
  print *, x2(2:5)
end program

```

In the program above, x1(2:5) is undefined, is x2(2:5) undefined or defined as zeros?

---

<div class="post-metadata">

**Author:** ![ivanpribec](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/ivanpribec/32/3290_2.png) [@ivanpribec](https://fortran-lang.discourse.group/u/ivanpribec)\
**Post date:** [June 12, 2022, 6:25pm UTC](https://fortran-lang.discourse.group/t/allocatable-array-defined-or-not/3736/2 "2022-06-12T18:25:35Z")

</div>

I don’t see any fundamental difference from your previous question: [Undefined variables](https://fortran-lang.discourse.group/t/undefined-variables/3708)

---

<div class="post-metadata">

**Author:** ![fortran4r](https://avatars.discourse-cdn.com/v4/letter/f/9de0a6/32.png) [@fortran4r](https://fortran-lang.discourse.group/u/fortran4r)\
**Post date:** [June 12, 2022, 6:35pm UTC](https://fortran-lang.discourse.group/t/allocatable-array-defined-or-not/3736/4 "2022-06-12T18:35:16Z")

</div>

It is a different question. I am uncertain whether assigning value to one element of an allocatable array will make the other elements defined as zeros.

---

<div class="post-metadata">

**Author:** ![rwmsu](https://avatars.discourse-cdn.com/v4/letter/r/48db29/32.png) [@rwmsu](https://fortran-lang.discourse.group/u/rwmsu)\
**Post date:** [June 12, 2022, 6:42pm UTC](https://fortran-lang.discourse.group/t/allocatable-array-defined-or-not/3736/5 "2022-06-12T18:42:17Z")

</div>

Just use sourced allocation to initialize arrays to zero and don’t worry about it.

```auto
allocate(x2(5), SOURCE=0.0d0)

```