题解 | #挑7#

#include<bits/stdc++.h>
using namespace std;
int main() {
    int n;
    while(cin>>n) {
        int count=0;    //记录与7有关的数字的个数
        for(int i=1;i<=n;i++) {
            if(i%7==0){    //该数是7的倍数
                count++;
                continue;
            }else if(i%10==7) {    //该数的个位数是7
                count++;
                continue;
            }else if(i%100/10==7) {    //该数的十位数是7
                count++;
                continue;
            }else if(i%1000/100==7) {//该数的百位数是7
                count++;
                continue;
            }else if(i%10000/1000==7) {//该数的千位数是7
                count++;
                continue;
            }
        }
        cout<<count<<endl;
    }
    return 0;
}