面试题32—从1到n整数中1出现的次数

题目：输入一个整数，求从1到n这n个数的十进制中1出现的次数。

代码示例：

#include<iostream>
using namespace std;
int NumOfOne(int n)
{
	if (n <= 0)
		return 0;
	int n_copy = n;
	int NumOfBit = 0;
	while (n_copy)
	{
		NumOfBit++;
		n_copy /= 10;
	}
	//

	int Base = 1;
	int bitnum = 1;
	int numofone = 0;

	while (bitnum<=NumOfBit)
	{
		if (bitnum == 1)
		{
			int former = n % 10;
			int Round = n / 10;
			numofone += former ? 1 : 0;
			numofone += Round*Base;
			Base *= 10;
			bitnum++;
		}
		else
		{
			int former = n%Base;
			int Round = n / (Base * 10);
			int weight = n % (Base * 10) / Base;
			if (weight > 1)
			{
				numofone += Round*Base + Base;
			}
			else if (weight == 1)
			{
				numofone += Round*Base + former + 1;
			}
			else
			{
				numofone += Round*Base;
			}
			Base *= 10;
			bitnum++;
		}
	}
	return numofone;
}

int main()
{
	int n;
	cout << "输入一个正数：";
	cin >> n;
	cout << 1 << "-" << n << "中1的个数总和为：" << NumOfOne(n) << endl;
}