Using srand(time(NULL)) in Swift gives compiler error

Swift uses nil for a NULL-pointer, and the return value of time() has to be cast to an UInt32:

srand(UInt32(time(nil))) 

But consider to use arc4random() or its variants instead. From http://nshipster.com/random/:

• arc4random does not require an initial seed (with srand or srandom), making it that much easier to use.
• arc4random has a range up to 0x100000000 (4294967296), whereas rand and random top out at RAND_MAX = 0x7fffffff (2147483647).
• rand has often been implemented in a way that regularly cycles low bits, making it more predictable.

For example,

let x = arc4random_uniform(10) 

generates a random number in the range 0 ... 9.

For some compilers this NULL==0 is not true. We are using NULL for pointers. Try this:

srand(time(0));