计算一个数是2，3，5的几次方

private static string GetPowerResult(int num)
{
    int x = 0, y = 0, z = 0;
    while (num % 2 == 0)
    {
        num = num / 2;
        x++;
    }
    while (num % 3 == 0)
    {
        num = num / 3;
        y++;
    }
    while (num % 5 == 0)
    {
        num = num / 5;
        z++;
    }

    if (num == 1)
        return String.Format("2^{0}*3^{1}*5^{2}", x, y, z);
    else
        return "您输入的数值无效";
}