arc4random VS arc4random_uniform(better)

• int value = arc4random() % x //获取0到x-1之间的整数

• int value = (arc4random() % x)+1//获取1到x之间的整数

• Random int between 0 and N - 1

  • int value = arc4random_uniform(N);// without modulo(余数) bias（某个数相比某些数会出现多次）.

• Random int between 1 and N

  • int value = arc4random_uniform(N) + 1;