pat 1049. Counting Ones (30)

看别人的题解懂了一些些    参考《编程之美》P132 页《1 的数目》

#include<iostream>
#include<stdio.h>
using namespace std;
int getone(int n)
{
	int ans=0,base=1,right,left,now;
	while(n/base)
	{
		right=n%base;
		left=n/(base*10);
		now=(n/base)%10;
		if(now==0)ans+=left*base;
		else
			if(now==1)ans+=left*base+right+1;
			else
				ans+=(left+1)*base;
         base*=10;
	}
	return ans;
}
int  main()
{
	int n;
	while(scanf("%d",&n)!=EOF)
	{
		printf("%d\n",getone(n));
	}
	return 0;
}