Evaluate binomial coefficients: Difference between revisions

=={{header|Windows Batch}}==

<lang dos>@echo off & setlocal

if "%~2"=="" ( echo Usage: %~nx0 n k && goto :EOF )

call :binom binom %~1 %~2

1>&2 set /P "=%~1 choose %~2 = "<NUL

echo %binom%

goto :EOF

:binom <var_to_set> <N> <K>

setlocal

set /a coeff=1, nk=%~2 - %~3 + 1

for /L %%I in (%nk%, 1, %~2) do set /a coeff *= %%I

for /L %%I in (1, 1, %~3) do set /a coeff /= %%I

endlocal && set "%~1=%coeff%"

goto :EOF</lang>

{{Out}}

<pre>

> binom.bat 5 3

5 choose 3 = 10

> binom.bat 100 2

100 choose 2 = 4950

</pre>

The string <code>n choose k = </code> is output to stderr, while the result is echoed to stdout. This should allow capturing the result with a <code>for /f</code> loop without needing to define tokens or delims.

But...

<pre>

> binom.bat 33 17

33 choose 17 = 0

> binom.bat 15 10

15 choose 10 = -547

</pre>

The Windows cmd console only handles 32-bit integers. If a factoral exceeds 2147483647 at any point, <code>set /a</code> will choke and roll over to a negative value, giving unexpected results. Unfortunately, this is as good as it gets for pure batch. It's probably better to employ a PowerShell or JScript helper or similar instead.