# checking input an integer greater than 0?

16 views (last 30 days)
Jens Petit-jean on 16 Nov 2020
Commented: John D'Errico on 17 Nov 2020
how can I check if my input is a integer greater than 0?

John D'Errico on 16 Nov 2020
Edited: John D'Errico on 16 Nov 2020
If you want to check for an integer that exceeds zero, first use the && and || operators.
So assuming you want to throw an error if it fails, then I might do...
if (x <= 0) || (rem(x,1) ~= 0)
error('Oh nO, Mr. Bill! x was not a positive integer.')
end
You use the || operator here, because MATLAB is more efficient with them in an if statement. They short circuit the test, so if the first part of the test is true, then there is no need to even execute the second clause in the test. The && operator works the same way.
I might even have added a test that x be a scalar variable.
If your question is you want to do something specifically if x is a positve integer, then another ay to write it would be:
if (numel(x) == 1) && (x > 0) && (fix(x,1) == 0)
disp('Happy days are here again...')
else
error('Oh nO, Mr. Bill! x was not a scalar positive integer.')
end
As you can see, I even added a test that x be scalar. There are of course alternative ways to test for an element being an integer. (fix(x)==x) is another, or (round(x) == x). Note that all such tests, when applied to a scalar are all extremely fast. Actually, the slowest of them is the rem test I used above.
You should also see that when I changed the if statement, I now had to use &&, which is the short-circuited version that applies.
James Tursa on 16 Nov 2020
Your first suggestion covers the x==inf case, but the second formulation doesn't.
John D'Errico on 17 Nov 2020
Good point. Best of course would be to explicitly test for inf or NaN input.

Ameer Hamza on 16 Nov 2020
Edited: Ameer Hamza on 16 Nov 2020
You can use this condition
tf = (x>0) & (round(x)==x)
Example
>> x = 5;
>> tf = (x>0) & (round(x)==x)
tf =
logical
1
>> x = 4.5;
>> tf = (x>0) & (round(x)==x)
tf =
logical
0
##### 3 CommentsShow 1 older commentHide 1 older comment
Ameer Hamza on 16 Nov 2020
Can you give an example of how it does work?
James Tursa on 16 Nov 2020
Doesn't cover the x==inf case.

Matt J on 16 Nov 2020
Edited: Matt J on 16 Nov 2020
validateattributes(yourInput,"numeric",{"integer","nonnegative"})
John D'Errico on 16 Nov 2020
"greater than 0"
validateattributes(yourInput,"numeric",{"integer","positive"})