Description:
The task is simple: given any positive integer N, you are supposed to count the total number of 1’s in the decimal form of the integers from 1 to N. For example, given N being 12, there are five 1’s in 1, 10, 11, and 12.
Input Specification:
Each input file contains one test case which gives the positive N (<=230).
Output Specification:
For each test case, print the number of 1’s in one line.
Sample Input:
12
Sample Output:
5
//NKW 甲级真题1038
#pragma warning(disable:4996)
#include <stdio.h>
#include <stdlib.h>
int main(){
int num, cnt = 0, a = 1, left, now, right;
scanf("%d", &num);
while (num/a){
left = num / (a * 10);
now = num / a % 10;
right = num % a;
if (now == 0) //0xxx
cnt += left * a;
else if (now == 1) //1xxx,1000、1001……1xxx
cnt += left*a + right + 1;
else //2xxx,1000、1001……1999
cnt += (left + 1)*a;
a *= 10;
}
printf("%d\n", cnt);
system("pause");
return 0;
}