/*
 * 1-n整數中１出現的次數.cpp
 *
 *  Created on: 2018年5月1日
 *      Author: soyo
 */
#include<iostream>
using namespace std;
int NumberOf1( unsigned int n)
{
   int number=0;
  while(n>=1)
   {
       if(n%10==1)
           number++;
       n=n/10;
   }
   return number;
}
int NumberOf1Between1AndN(unsigned int
 
 n)
{
    unsigned int i;
    int number=0;
    for(i=0;i<=n;i++)
    {
        //cout<<i<<" ";
       number+=NumberOf1(i);
    }
    return number;
}
int main()
{
    unsigned int n;
    cin>>n;
    int num;
    num=NumberOf1Between1AndN(n);
    cout<<endl;
    cout<<"
 
Num中１的個數為:"<<num<<endl;
}

結果:

100
Num中１的個數為:21

從１到N的整數中１出現的次數