iOS random number

iOS has the following three random number methods:

1. Srand ((unsigned) time (0)); Without this sentence, the random number that is generated every time.
int i = rand ()% 5;

2. Srandom (Time (0));
int i = random ()% 5;

3. int i = arc4random ()% 5;

Note: rand () and random () are not actually a true pseudo-random number generator, it is necessary to initialize the random seed before use, or the random number generated each time.

Arc4random () is a true pseudo-random algorithm that does not need to generate random seeds because it is generated automatically when the first call is called. And the range is twice times that of Rand (). In the iphone, Rand_max is 0x7fffffff (2147483647), and Arc4random () returns the maximum value is 0x100000000 (4294967296).

Accuracy comparison: arc4random () > Random () > rand ().

Common methods: Arc4random

1. Get a random integer range in: [0,100] including 0, excluding 100

int x = arc4random ()% 100;

2. Get a random number range in: [500,1000], including 500, excluding 1000

int y = (arc4random ()% 501) + 500;

3. Get a random integer range in [From,to], including from, excluding to

-(int) GetRandomNumber: (int) from to: (int.) to

{

return (int) (from + (Arc4random ()% (To–from + 1));

}

Actually, this is good.

Nstimeinterval time=[[nsdate Date] timeintervalsince1970]*1000;

Double i=time; Nstimeinterval returns a double type

iOS random number