孪生素数对

#include <stdio.h>
#include <math.h>
int isPrime (int N);
int main() {
	int M;
	while (scanf("%d",&M) !=EOF) {
		int cishu=0;
		int first=0;
		int second=0;
		for (int j=2;j<=M;j++) {
			if (isPrime(j)){
				second=first;
				first=j;
				if((first-second)==2 && (first!=0 && second !=0)){
					cishu++;
					
				}
				//printf("%d___%d\n",first,second);
			}
			

		}
		printf("%d",cishu);

	}


	return 0;
}
int isPrime (int N) {
	if (N <=3) {
		return N>1;
	} 

	if (N%6 != 1 && N%6 != 5) {
		return 0;
	}
	int ss=(int)sqrt((double)N)+1;
	for(int i=5; i <= ss; i+=6) {
		if (N%i ==0 || N%(i+2) ==0) {
			return 0;
				
		}
	}
	return 1;
}

原创不易，转载的时候带上帖子地址。