个人学习记录，代码难免不尽人意。

reversible prime in any number system is a prime whose “reverse” in that number system is also a prime. For example in the decimal system 73 is a reversible prime because its reverse 37 is also a prime.

Now given any two positive integers N (<10 5) and D (1<D≤10), you are supposed to tell if N is a reversible prime with radix D.

Input Specification:
The input file consists of several test cases. Each case occupies a line which contains two integers N and D. The input is finished by a negative N.

Output Specification:
For each test case, print in one line Yes if N is a reversible prime with radix D, or No if not.

Sample Input:
73 10
23 2
23 10
-2
Sample Output:
Yes
Yes
No

#include<cstdio>
#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<cmath>
using namespace std;
bool isprime(int num){if(num<=1) return false;int n=(int)sqrt(num*1.0);for(int i=2;i<=n;i++){if(num%i==0) return false;}return true;}
int changeandreverse(int n,int radix){int m=0;while(n!=0){m=m*radix+(n%radix);n/=radix;}return m;
}
int main(){int n,radix;scanf("%d",&n);while(n>=0){scanf("%d",&radix);int re_n=changeandreverse(n,radix);if(isprime(n)&&isprime(re_n)) printf("Yes\n");else printf("No\n");scanf("%d",&n);}return 0;
}

本题重点掌握判断素数的方法以及sprt函数只能对浮点数进行运算。