Write a program to check whether a given number is an ugly number.
Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 6, 8 are ugly while 14 is not ugly since it includes another prime factor 7.
Note that 1 is typically treated as an ugly number.
丑陋数就是其质数因子只能是2,3,5。那么最直接的办法就是不停的除以这些质数，如果剩余的数字是1的话就是丑陋数
static public bool IsUgly(int num) {while (num >= 2) {if (num % 2 == 0) num /= 2;else if (num % 3 == 0) num /= 3;else if (num % 5 == 0) num /= 5;else return false;}return num == 1;}