Batch- generating a random number of random numbers - batch-file

Question

As part of a program I'm making, I want to be able to 'plot' or 'mark' random points on a grid. In doing so I need to generate a random number(x) to determine the number of plots- and then x amount of different random numbers representing coordinates. At the moment I have the following code:
#echo off
:obno
set /a r1=%random%
if %r1% gtr 10 goto obno else (
goto ob
)
:ob
for /L %%R in (1,1,%r1%) do set /a n%%R=%random%*240/32678+1
echo %r1%
echo %n1% %n2% %n3% %n4% %n5% %n6% %n7% %n8% %n9% %n10%
pause
What happens here is I end up with x amount of the same random number instead of different ones
i.e. ouput:
5
108 108 108 108 108
so any help would be greatly appreciated!

Answer 1

In a loop you should be using delayed expansion e.g.
SETLOCAL ENABLEDELAYEDEXPANSION and using !RANDOM! instead of %RANDOM%
And...
%RANDOM% gives you a random number between 0 and 32767.
Using an expression like below you can change the range to anything you like (here the range is [1…100] instead of [0…32767]).
SET /A test=%RANDOM% * 100 / 32768 + 1
And below will produce number between 1~100
set /a num=%random% %%100 +1
To get a random number between 0 and 9 on the command line, use
set /a "rand=%random% % 10"
If used in a batch file then double the modulo operator
set /a "rand=%random% %% 10"

Answer 2

Using your code, you can use a call and double the % to make %%random%%
#echo off
:obno
set /a r1=%random%
if %r1% gtr 10 goto obno else (
goto ob
)
:ob
for /L %%R in (1,1,%r1%) do call set /a n%%R=%%random%%*240/32678+1
echo %r1%
echo %n1% %n2% %n3% %n4% %n5% %n6% %n7% %n8% %n9% %n10%
pause

Answer 3

Here is a simliar post to generate random numbers in a batch file
You need to include the following at the start of your batch file
setlocal EnableDelayedExpansion
Random variable not changing in "for" loop in windows batch file

Answer 4

#ECHO OFF
SETLOCAL
:obno
set /a r1=%RANDOM% %% 10 + 1
:ob
for /L %%R in (1,1,%r1%) do CALL set /a n%%R=%%random%% %%%% 240 + 1
echo %r1%
echo %n1% %n2% %n3% %n4% %n5% %n6% %n7% %n8% %n9% %n10%
GOTO :EOF
Since %random% produces a random number 0..32767, your original code will waste a lot of time waiting for a number between 0 and 10. Also, it may generate 0.
The % operator is used for 'modulus'. Within a batch, you need to double it, so %random% %% 10 produces 0..9
By CALLing a command, you can avoid the need to setlocal enabledelayedexpansion BUT you also need to redouble any % you use, hence the doubling around random and quadrupling for the mod operator.
The setlocal isn't strictly necessary, BUT what it does is back out enviroment changes when the batch ends, so r1,n1..n10 simply no longer exist in the environment once the batch finishes. If you OMIT the setlocal then any variable set in one run will REMAIN set for a subsequent run, so if your first run sets n5 (and also therefore n1..n4) then if the second run sets r1=2, n3..n5 would be displayed with the stale data from the previous run.
Finally, if you allow r1=0 then since none of n1..n10 are set, the echo %n1%... command will be resolved to echo, will will show the echo status (Echo is on/off). This can be overcome by using the syntax echo(%n1%.... The character directly following the O has been found to do some strange things.
echoDot for instance is traditional for a blak newline. The ( may look odd and appear to 'unbalance' the nesting, but works quite happily to produce a newline with empty arguments.