执行while循环（Java）

Question

我正在尝试编写一个程序来对每个 4 位数字的每个数字求和。例如，我从 1000 开始，添加 1001 后，千位变为 2，百位变为 0，十位变为 0，个位变为 1。这应该继续添加每个数字，直到达到 9999。这是我的代码，它只输出 9999。

int num = 1000, unit = 0, ten = 0, hundred = 0, thousand = 0, newNum = 0, sumth = 0, sumh = 0, sumten = 0, sumu = 0;

while (num <= 9999)
{
    unit = num%10;
    newNum = num/10;
    ten = newNum%10;
    newNum=newNum/10;
    hundred = newNum%10;
    thousand = newNum/10;
    num++;
}
sumth = thousand + sumth;
sumh = hundred + sumh;
sumten = ten + sumten;
sumu = unit + sumu;

System.out.println(sumth + " " + sumh + " " + sumten + " " + sumu);

Answer 1

为了便于阅读，稍微整理一下：

int num = 1000,
    sumThousands = 0,
    sumHundreds = 0,
    sumTens = 0,
    sumUnits = 0;

    while (num <= 9999)
    {
        int units = num % 10;
        int tens = (num / 10) % 10;
        int hundreds = (num / 100) % 10;
        int thousands = (num / 1000) % 10;

        sumUnits += units;
        sumTens += tens;
        sumHundreds += hundreds;
        sumThousands += thousands;

        num++;
    }

System.out.println(sumThousands + " " + sumHundreds + " " + sumTens + " " + sumUnits);

你会得到的输出是：

45000 40500 40500 40500

这是意料之中的。对于整数序列 1000..9999：

• 在千位列中，每个数字 1..9 重复 1000 次
  • 所以千和是1000(9+8+7+6+5+4+3+2+1) = 1000(9(10)/2) = 45000
• 在每隔一列中，每个数字 0..9 重复 900 次
  • 所以其他列的总和是900(9+8+7+6+5+4+3+2+1) = 900(9(10)/2) = 40500

Answer 2

应该在while loop里面移动

while (num <= 9999)
    {
        unit = num%10;
        newNum = num/10;
        ten = newNum%10;
        newNum=newNum/10;
        hundred = newNum%10;
        thousand = newNum/10;

        sumth = thousand + sumth;
        sumh = hundred + sumh;
        sumten = ten + sumten;
        sumu = unit + sumu
        num++;    

    }

输出：45000 40500 40500 40500
工作链接：https://ideone.com/WrAX8D