random BOOLs in an efficient way for cocos2d

Question

According to Steffen's post this is an efficient way to generate random BOOLs in cocos2d

+(BOOL) getYesOrNo
{
   return (CCRANDOM_0_1() < 0.5f);
}

but how do I set a range for this? (e.g. 0 - 29 is the interval and 5 ones BOOL = NO, 25 ones BOOL = YES )

score 13 · Accepted Answer · answered Feb 06 '12 at 10:26

13

you can do something like this:

+(BOOL) getYesOrNo
{
    int tmp = (arc4random() % 30)+1;
    if(tmp % 5 == 0)
        return YES;
    return NO;
}

answered Feb 06 '12 at 10:26

nicoz_88

456
3
9

This has modulo bias. – Alexander Aug 23 '16 at 15:52
4

This solution produces false values more than true values, something like 1:10 for false value and that's because the percentage of making 5,10,15,20,25,30 is like 6/30 which make no sense at all – Ali Omari Jan 22 '17 at 13:41

score 3 · Answer 2 · answered Feb 06 '12 at 12:16

You should use arc4random for random number generator.

#include <stdlib.h>

     u_int32_t
     arc4random(void);

The arc4random() function uses the key stream generator employed by the arc4 cipher, which uses 8*8 8 bit S-Boxes. The S-Boxes can be in about (2*1700) states. The arc4random() function returns pseudo- random numbers in the range of 0 to (2*32)-1, and therefore has twice the range of rand and random.

-(BOOL)foo4random
{
u_int32_t randomNumber = (arc4random() % ((unsigned)RAND_MAX + 1));
if(randomNumber % 5 ==0)
    return YES;
return NO;

}

For more information on arc4random type

man arc4random

on terminal.

You should use `arc4random_uniform` to prevent modulo bias, rather than reinventing the wheel — Alexander, Aug 23 '16 at 15:54

score 0 · Answer 3 · answered Jan 09 '19 at 13:18

0

The following code will generate a random bool value:

-(BOOL) randomBool
{
    int tmp = (arc4random() % 10);
    if(tmp % 2 == 0)
        return YES;
    return NO;
}

answered Jan 09 '19 at 13:18

Darius Miliauskas

3,391
4
35
53

random BOOLs in an efficient way for cocos2d

3 Answers3