[Project Euler]加入欧拉 Problem 7

By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6^(th) prime is 13.

What is the 10001^(st) prime number?

 

求第10001个质数。 这个比较简单，使用一个循环就出来了，不到2秒。

欧拉项目第七题#include <stdio.h>

#include <stdlib.h>

#include <math.h>

#include <stdbool.h>



bool isPrime(double num);



int main(int argc, char *argv[])

{

    int n = 0;

    double num = 2.0;

    

    while(1)

    {

        if(isPrime(num))

        {

            n++;

            if(n == 10001)

            break;

        }

        num++;

    } 

    

  printf("%lf", num);

  system("PAUSE");	

  return 0;

}



bool isPrime(double num)

{

    double sqr = sqrt(num + 1);

    

    unsigned long i = 2;

    for(i = 2; i <= sqr; i++)

    {

        if(fmod(num, i) == 0)

        return false;

    }

    

    return true;

}