# Integer check

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Andy on 21 Sep 2011
Commented: Stephen Cobeldick on 16 Sep 2019
How can i do an integer check in matlab? Say i have a number, a = 1.5, how do i check if it is integer or not? i want to use an if statement:
if non_integer(a) == true
end
so i need to know what to use for "non_integer", which would return a true or false

Sean de Wolski on 21 Sep 2011
floor(x)==x

Walter Roberson on 21 Sep 2011
Fails on inf and -inf ;-)
Jukka Kaipala on 27 Jul 2016
Like it should. Inf is not considered an integer, and the same goes for NaN.
Thorsten on 2 Nov 2016
Like it should not. Because Inf is not an integer, but
floor(inf) == inf
returns true.
So the correct test would be
~isinf(x) & floor(x) == x
Or, as Walter suggests,
mod(x,1) == 0
But this may be all just of theoretical interest.

Walter Roberson on 21 Sep 2011
I suggest you think about floor(), ceil(), fix(), and round()

Walter Roberson on 21 Sep 2011
A test that works even for nan and inf and -inf :
mod(x,1) == 0
Walter Roberson on 2 Nov 2016
NaN == 0 is false, so in each of those cases, the result of the test would be false, indicating that the values are not integers.
But if you tried the one above, floor(inf)==inf then the result would be true, seemingly indicating that it is an integer when it is not.

Fandi Bataineh on 2 Feb 2019
Edited: Fandi Bataineh on 2 Feb 2019
use
floor(x)==ceil(x)
this will be true only for integers

#### 1 Comment

Sivyer Ge on 24 Feb 2019
Actually this will not work for type 'char'. Do you know other way to identify the difference between char and integer?

Manuel Alcazar on 16 Sep 2019
function [bool,idx] = isint(x)
% Check whether input is integer or not
% Inf and NaN are not integers
if ~isnumeric(x)
error('Input must be a numeric, not a %s.',class(x))
end
bool = (mod(x,1) == 0);
% bool = (round(x) == floor(x)); % Other approach. Fails with Inf and
% NaN.
idx = find(bool);
% Manolín Sept-2019
end

per isakson on 16 Sep 2019
function isf = isflint( m )
% floating double only
%
assert( isa( m, 'double' ) && isvector( m ) ...
, 'isflint:IllegalInput' ...
, 'The input should be a double vector' )
isf = all( abs( m ) <= flintmax ) ...
&& all( floor( m ) == m ) ;
end

#### 1 Comment

Stephen Cobeldick on 16 Sep 2019
This could be trivially vectorized: why force it to return a scalar?