How to create a random float in Objective-C?

Question

I'm trying to create a random float between 0.15 and 0.3 in Objective-C. The following code always returns 1:

int randn = (random() % 15)+15;
float pscale = (float)randn / 100;

What am I doing wrong?

Solution 1

Try this:

 (float)rand() / RAND_MAX

Or to get one between 0 and 5:

 float randomNum = ((float)rand() / RAND_MAX) * 5;

Several ways to do the same thing.

Solution 2

Here is a function

- (float)randomFloatBetween:(float)smallNumber and:(float)bigNumber {
    float diff = bigNumber - smallNumber;
    return (((float) (arc4random() % ((unsigned)RAND_MAX + 1)) / RAND_MAX) * diff) + smallNumber;
}

Solution 3

1. use arc4random() or seed your random values

2. try

   float pscale = ((float)randn) / 100.0f;
   

Solution 4

Your code works for me, it produces a random number between 0.15 and 0.3 (provided I seed with srandom()). Have you called srandom() before the first call to random()? You will need to provide srandom() with some entropic value (a lot of people just use srandom(time(NULL))).

For more serious random number generation, have a look into arc4random, which is used for cryptographic purposes. This random number function also returns an integer type, so you will still need to cast the result to a floating point type.

Solution 5

Easiest.

+ (float)randomNumberBetween:(float)min maxNumber:(float)max
{
    return min + arc4random_uniform(max - min + 1);
}

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