Usage of random numbers in OC (arc4random (), random (), and ccrandom_0_1 ()

1) arc4random () is more accurate and does not need to be generated immediately.

Usage:

The code for getting an integer between 0 and X-1 through arc4random () is as follows:

Int value = arc4random () % x;

The code for getting an integer between 1 and X is as follows:

Int value = (arc4random () % x) + 1;

 

2). It is used in ccrandom_0_1 () cocos2d and the range is [0, 1].

Usage:

Float random = ccrandom_0_1 () * 5; // [] ccrandom_0_1 () value range: []

 

3) set the seed when random () needs Initialization

Usage:

Srandom (unsigned INT) Time (time_t *) null); // set the seed during initialization.

 

 

Rand () is not a real pseudo-random number generator. Random () is relatively good, but not ideal. Fortunately, there are other options on the iPhone. Personally, I prefer arc4random () because it is a real pseudo-random algorithm and the range is twice that of rand.

 

 

-(float)randomFloatBetween:(float)num1 andLargerFloat:(float)num2
{
    int startVal = num1*10000;
    int endVal = num2*10000; 

    int randomValue = startVal +(arc4random()%(endVal - startVal));
    float a = randomValue;

    return(a /10000.0);
}

In the source code of some products, such statements are often found,

Srand (unsigned (Time (null )));

Why is this actually quite simple.

1. The time () function indicates the number of seconds from 00:00:00 to the current time. The time (null) function indicates obtaining a time. To be precise, it indicates obtaining a pointer address.

2. The srand () function generates random number seeds. When the random number rand () is called, he will check that if the user has called srand (SEED) before, he will call srand (SEED) again) to generate random seed. If srand (SEED) is not called, srand (1) is automatically called once. Therefore, if you want rand () to generate different values for each call, you need to call srand (SEED) once each time, and seed cannot be the same.

Based on the above two points, it is very clear.

Srand (unsigned (Time (null) indicates that random seed is generated to ensure that random values are not repeated when rand () is called.

Usage of random numbers in OC (arc4random (), random (), and ccrandom_0_1 ()