Random Number Problem in Objective-C

Question

I am trying to create a random number between 0 and the size of my array:

    float randomNum = (rand() / RAND_MAX) * [items count];
    NSLog(@"%f",randomNum);
    NSLog(@"%d",[items count]);

randomNum is always 0.0000000

Answer 1

Try this instead:

int randomNum = arc4random() % ([items count] +1);

note that randomNumit will not be used as an array reference. For this you want:

int randomRef = arc4random() % [items count];
id myRandomObject = [myArray objectAtIndex:randomRef];

arc4random()returns u_int32_t(int), which makes it easy to transfer to things like bones, arrays and other problems of the real world, unlikerand()

Answer 2

randomNum is always 0.0000000

This is because you are doing integer division instead of floating point division; (rand() / RAND_MAX)will almost always be 0. (Exercise to the reader: when is it not 0?)

Here is one way to fix this:

float randomNum = ((float)rand() / (float)RAND_MAX) * [items count];

arc4random.

Answer 3

, 0 , :

randomNum = random() % [items count];  // between 0 and arraySize-1

If you want your array size to include:

randomNum = random() % ([items count]+1);  // between 0 and arraySize

Answer 4

Try rand() * [items count];

IIRC, rand()returns values ​​from 0 to 1.

Answer 5

people say arc4random () is the best rnd method ...

you can use it this way to get a number in the range:

int fromNumber = 0;
int toNumber = 50;
float randomNumber = (arc4random()%(toNumber-fromNumber))+fromNumber;
NSLog(@"random number is:  %f",randomNumber); // you'll get from 0 to 49

...

int fromNumber = 12;
int toNumber = 101;
float randomNumber = (arc4random()%(toNumber-fromNumber))+fromNumber;
NSLog(@"random number is:  %f",randomNumber); // you'll get from 12 to 100

Answer 6

Before using rand (), you must set the seed, you do this by calling the srand function and passing the seed.

See here for srand documentation and here for rands.