# About isinteger command(confusion)

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C Zeng on 14 Mar 2013
Edited: per isakson on 16 Jan 2015
Hi, by the command of isinteger I can check if it is an integer, however, when defined at first, Matlab assume it is double precision right? So even a=3, isinteger(a) returns 0.
How to solve this problem?

per isakson on 14 Mar 2013
Edited: per isakson on 16 Jan 2015
Matlab represents integers in differnt ways:
• int8, int16, etc. see Christians answer
• with a special use of double, which is called flint. See Floating Points
I use this function to test for flint
function isf = isflint( m )
% floating double only
try
bitand( abs( m ), 1 );
isf = true;
catch me
isf = false;
end
end
I picked up the idea from a contribution by the "Pedestrian" in the FEX.
(I stripped off comments and error handling.)
Jan on 16 Mar 2013
The problem is to decide, if 1e17 is an integer or not: Because a double can store 16 digits only, this number does not contain any information about the fractional part for reasons of the precision. bitand() detect this and throw an error, while 1e17==round(1e17) replies true, because cropping the fractional part does not influence value.
C Zeng on 17 Mar 2013
Thanks, I understand it. It is good to know.

### More Answers (2)

Jan on 16 Mar 2013
Joining the rounding with the checks for overflows:
function isf = isflint(m)
isf = (abs(m) <= bitmax && m == floor(m));
per isakson on 18 Mar 2013
I'll replace my cryptic isflint.

ChristianW on 14 Mar 2013
doc isinteger
isinteger(int8(3))
Jan on 16 Mar 2013
@C Zeng: @(x) x==round(x) is an anonymous function. You find an exhaustive description ion the documentation.
C Zeng on 17 Mar 2013
OK