An Octave cookbook. Each entry should go in a separate section and have the following subsection: problem, solution, discussion and maybe a see also.
Find if a number is even/odd
You have a number, or an array or matrix of them, and want to know if any of them is an odd or even number, i.e., their parity.
Check the remainder of a division by two. If the remainder is zero, the number is odd.
mod (value, 2) ## 1 if odd, zero if even
mod() acceps a matrix, the following can be done:
any (mod (values, 2)) ## true if at least one number in values is even all (mod (values, 2)) ## true if all numbers in values are odd any (!logical (mod (values, 2))) ## true if at least one number in values is even all (!logical (mod (values, 2))) ## true if all numbers in values are even
Since we are checking for the remainder of a division, the first choice would be to use
rem(). However, in the case of negative numbers
mod() will still return a positive number making it easier for comparisons. Another alternative is to use
bitand (X, 1) or
bitget (X, 1) but those are a bit slower.
Note that this solution applies to integers only. Non-integers such as 1/2 or 4.201 are neither even nor odd. If the source of the numbers are unknown, such as user input, some sort of checking should be applied for NaN, Inf, non-integer values.
Find if a number is an integer.