7-1 Prime Day (20分)

The above picture is from Sina Weibo, showing May 23rd, 2019 as a very cool “Prime Day”. That is, not only that the corresponding number of the date 20190523 is a prime, but all its sub-strings ended at the last digit 3 are prime numbers.

Now your job is to tell if a given date is a Prime Day.
Input Specification:

Each input file contains one test case. For each case, a date between January 1st, 0001 and December 31st, 9999 is given, in the format yyyymmdd.
Output Specification:

For each given date, output in the decreasing order of the length of the substrings, each occupies a line. In each line, print the string first, followed by a space, then Yes if it is a prime number, or No if not. If this date is a Prime Day, print in the last line All Prime!.

Sample Input 1:

20190523

Sample Output 1:

20190523 Yes
0190523 Yes
190523 Yes
90523 Yes
0523 Yes
523 Yes
23 Yes
3 Yes
All Prime!

Sample Input 2:

20191231

Sample Output 2:

20191231 Yes
0191231 Yes
191231 Yes
91231 No
1231 Yes
231 No
31 Yes
1 No

题意很清晰，可以使用substr()函数方便截取字符串，还有stoi()函数把字符串转成数字
AC代码

#include<iostream>
using namespace std;

string date;

bool is_prime(string s)
{
    int res=stoi(s);
    if(res==1||res==0)return false;
    for(int i=2;i*i<=res;++i)if(res%i==0)return false;

    return true;
}

int main()
{
    cin>>date;
    int cnt=0;
    for(int i=0;i<date.size();++i)
    {
        string temp=date.substr(i);
        if(is_prime(temp))
        {
            cout<<temp<<' '<<"Yes"<<endl;
            cnt++;
        }
        else cout<<temp<<' '<<"No"<<endl;
    }
    if(cnt==date.size())puts("All Prime!");

    return 0;
}