C/C++ prob function

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ID:277928
 
Aug 7 2008, 11:44 am
Whats the best way to do what DM does, in C/C++ for probability. ie
if(prob(number))
I cant find any existing function, so what would be the best way to program something similar?
Aug 7 2008, 11:52 am
I don't remember what the name of the randomization function is in C/C++, so I'll just use rand(). This should work:
//I *think* it should be bool. I'm not sure.
bool prob(int n)
{
    //The addition of one is to make sure that prob(0) is
    //always going to return false.
    return n >= ((rand() + 1) % 100);
}
Aug 7 2008, 11:59 am
In response to Popisfizzy
Then i guess you don't know what i need to #include to use rand()(meaning the actual randomizer)?
Aug 7 2008, 1:22 pm
In response to Chibi-Gohan0
#include <cstdlib>

That has the rand function.

George Gough
Aug 7 2008, 1:26 pm
In response to KodeNerd
KodeNerd wrote:
#include <cstdlib>

That has the rand function.

George Gough

Thanks, i dont seem to have it though, know where i can get it?
Aug 7 2008, 1:26 pm
In response to Chibi-Gohan0
Aug 7 2008, 1:52 pm
In response to A.T.H.K
To clarify, cstdlib is suposed to be a standard lib in visual C++, which i have. But i dont have the file.
Aug 7 2008, 1:57 pm
In response to Chibi-Gohan0
Aug 7 2008, 2:01 pm
In response to A.T.H.K
I saw most of those, and if you take note to the first one is what i was talking about where the guy redirected him to stdlib.h. Anyway, Thanks.
Aug 7 2008, 2:03 pm
In response to A.T.H.K
Thanks for you help, i found the problem: cstdlib is for .cpp files only. i was using a .c file >.<
Aug 7 2008, 2:05 pm
In response to Chibi-Gohan0
Hehe nice i didn't really help lol, have fun.
Aug 7 2008, 2:06 pm
In response to Popisfizzy
Now that i have everything i need for rand(). Your function isnt working. i tested with if(prob(0)) and the following line was still executed(and actually, its executed every time no matter what the input).
Aug 7 2008, 2:12 pm
In response to Chibi-Gohan0
Do not forget to seed the random function generator.

George Gough
Aug 7 2008, 2:13 pm
In response to KodeNerd
Oh?
Aug 7 2008, 2:16 pm
In response to Chibi-Gohan0
The function is set to the default seed and will always give the same list of results unless you set the seed. I think the function is srand(unsigned int) or something along that line.

Setting the seed once is best IIRC.

George Gough
Aug 7 2008, 2:19 pm
In response to KodeNerd
So, is the seed inside the paramaters of srand() or is srand(paramater) the seed itself?
Aug 7 2008, 2:23 pm
In response to Chibi-Gohan0
The function is called as so:

const unsigned int some_number = 10;
srand(some_number);


George Gough
Aug 7 2008, 2:25 pm
In response to KodeNerd
Alright, one last thing. I get the following error after that is compiled:
error: void value not ignored as it ought to be
Aug 7 2008, 2:30 pm
In response to Chibi-Gohan0
Can you post the line that has that warning on it?

George Gough
Aug 7 2008, 2:33 pm
In response to KodeNerd
Its the one Pop made:
bool prob(int n) {
//The addition of one is to make sure that prob(0) is
//always going to return false.
const unsigned int num = 10;
return n >= ((srand(num) + 1) % 100); //<-------
}
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