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Topic: BEGINNER (Read 1052 times) |
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leslie griffin
Guest
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Re: BEGINNER
« Reply #2 on: Mar 30th, 2010, 9:25pm » |
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Thx for the help with the RND selection.I looked at your page on RND and tried my own variation on choosing 6 numbers.
dim drw(7)
cnt=0
dim lot(49)
for a=1 to 49
lot(a)=a
next
repeat
r=rnd(49)
if lot(r) then drw(cnt)=r lot(r)=0 print drw(cnt): cnt=cnt+1
until cnt=7
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admin
Administrator
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Posts: 1145
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Re: BEGINNER
« Reply #3 on: Mar 30th, 2010, 10:04pm » |
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on Mar 30th, 2010, 9:25pm, Guest-leslie griffin wrote:| Thx for the help with the RND selection.I looked at your page on RND and tried my own variation on choosing 6 numbers |
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I'm no mathematician, but I worry about the effect of that approach (discarding numbers if they've already been chosen) on the statistics. It also has the disadvantage of taking a variable time to complete.
The algorithm I listed more accurately reflects what a genuine lottery machine does - at each stage it makes a selection only from the remaining numbers.
It may not matter for your application, but unless you're very confident about the implications it's safer to stick with tried-and-tested algorithms. Anything to do with 'random' numbers is beset with pitfalls for the unwary.
Richard.
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leslie griffin
Guest
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Re: BEGINNER
« Reply #4 on: Mar 30th, 2010, 10:31pm » |
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Thx Richard..Makes sense.
i
I do appreciate that you give your time to answer and give advice to basic,pardon the pun, programmers like myself.
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L GRIFFIN
Guest
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Re: BEGINNER
« Reply #5 on: Mar 30th, 2010, 11:44pm » |
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I could not see how your prog. checked for duplicates, I thought I was missing something really deep in the code.
Put the code in a loop and it churned out duplicates at random.
for q= 1 to 40
max = 49
num = 6
dim lotto(max)
for I = 1 to max
lotto(I) = I
next I
for choice = 1 to num
R = rnd(max)
print lotto(R);
lotto(R) = max
max = max-1
next choice
print
next
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Ken Down
Guest
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Re: BEGINNER
« Reply #6 on: Mar 31st, 2010, 04:04am » |
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For the sake of readability, use upper case for BASIC keywords and lower case for variables.
Did you realise that you can have more than one DIM statement on a line? eg:
DIMx%(5),a$(3),z%50
Integer variables run just slightly faster than real variables, so numeric variables of the form x% or
draw%(20) are better where speed may be important.
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David Williams
Developer
member is offline
meh
Gender: 
Posts: 452
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Re: BEGINNER
« Reply #7 on: Mar 31st, 2010, 04:10am » |
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on Mar 31st, 2010, 04:04am, Guest-Ken Down wrote:| Integer variables run just slightly faster than real variables, so numeric variables of the form x% ... are better where speed may be important. |
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And the (capital letter) static integer variables (A%, B%, C%, ..., Z%) may be even better in that case.
David.
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admin
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Posts: 1145
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Re: BEGINNER
« Reply #8 on: Mar 31st, 2010, 08:38am » |
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on Mar 30th, 2010, 11:44pm, Guest-L GRIFFIN wrote:| I could not see how your prog. checked for duplicates |
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It works exactly like a lottery machine: it picks the first number from the full set of 49, then it picks the second number from the remaining 48, then it picks the third number from the remaining 47, etc. Hence it doesn't generate duplicates.
Quote:| Put the code in a loop and it churned out duplicates at random. |
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You're right - there was a bug in the code! The line:
Code:
should be:
Code:
Sorry about that.
Richard.
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admin
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Posts: 1145
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Re: BEGINNER
« Reply #9 on: Mar 31st, 2010, 09:01am » |
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on Mar 31st, 2010, 04:04am, Guest-Ken Down wrote:| Integer variables run just slightly faster than real variables, so numeric variables of the form x% or draw%(20) are better where speed may be important. |
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Integer variables may run faster than real variables, but that is not a relevant comparison in this case because the OP is not using real variables but variant variables (he is storing integer values in the variables). Integer variables do not run significantly faster than variant variables (and they make the program longer):
Code: i = 123456
i% = 123456
TIME = 0
FOR I% = 1 TO 1000000
j = i + i + i + i + i + i + i + i + i + i : NEXT
PRINT TIME
TIME = 0
FOR I% = 1 TO 1000000
j% = i% + i% + i% + i% + i% + i% + i% + i% + i% + i% : NEXT
PRINT TIME
It's true that the static integer variables do run faster, but that's a separate issue.
Note that Acorn versions of BBC BASIC don't have variant variables, so with those there may well be a speed advantage in using integer variables rather than real variables. However this group is specific to BBC BASIC for Windows which, like BBC BASIC (Z80) and BBC BASIC (86) has variant variables.
Richard.
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admin
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Posts: 1145
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Re: BEGINNER
« Reply #10 on: Mar 31st, 2010, 09:10am » |
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on Mar 31st, 2010, 04:04am, Guest-Ken Down wrote:| For the sake of readability, use upper case for BASIC keywords and lower case for variables. |
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The preferred naming convention is lower case for local (and private) variables, capitals for constants and a mixture of lower and upper case for global variables.
Because BBC BASIC for Windows supports asynchronous interrupts (e.g. ON SYS and ON TIME) it is important that global and local variables never share the same name. Because you don't (in principle) know what variable names are used in libraries and other CALLed or INSTALLed modules, adhering to a strict naming convention is the only guarantee of that.
Richard.
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