How to select range of values when using arc4random()

As pointed out in other posts below, it is better to use arc4random_uniform. (When this answer was originally written, arc4random_uniform was not available). Besides avoiding the modulo bias of arc4random() % x, it also avoids a seeding problem with arc4random when used recursively in short timeframes.

arc4random_uniform(4)

will generate 0, 1, 2 or 3. Thus you could use:

arc4random_uniform(51)

and merely add 50 to the result to get a range between 50 & 100 (inclusive).

To expand upon JohnK comment.

It is suggested that you use the following function to return a ranged random number:

arc4random_uniform(51)

which will return a random number in the range 0 to 50.

Then you can add your lower bounds to this like:

arc4random_uniform(51) + 50

which will return a random number in the range 50 to 100.

The reason we use arc4random_uniform(51) over arc4random() % 51 is to avoid the modulo bias. This is highlighted in the man page as follows:

arc4random_uniform(upper_bound) will return a uniformly distributed random number less than upper_bound. arc4random_uniform() is recommended over constructions like ``arc4random() % upper_bound'' as it avoids "modulo bias" when the upper bound is not a power of two.

In short you get a more evenly distributed random number generated.

int fromNumber = 10;int toNumber = 30;int randomNumber = (arc4random()%(toNumber-fromNumber))+fromNumber;

Will generate randon number between 10 and 30, i.e. 11,12,13,14......29