c++ - 如何从 C++ 中的斐波那契数列中提取质数？

Question

请帮助我的代码如下。我已经成功地找到了一个范围内的斐波那契数列，但我发现很难从斐波那契数列中提取素数。质数部分似乎有很多错误。请帮忙。谢谢

#include<iostream.h>
#include<conio.h>

void main()
{
  clrscr();
  int n, c, first = 0, second = 1, next, flag;

  cout << "Enter the number of terms of Fibonacci series you want" << endl;
  cin >> n;

  cout << "First " << n << " terms of Fibonacci series are :- " << endl;

  for (c = 0; c < n; c++)
  {
    if (c <= 1)
      next = c;
    else
    {
      next = first + second;
      first = second;
      second = next;
    }
    cout << next << endl;
    for (int j = 2; j<next; j++)
    {
      if (next%j == 0)
      {
        flag++;
      }
      if (flag == 0)
      {
        cout << "Prime numbers are" << next << "\t";
      }
    }
    getch();
  }
}

Answer 1

根据 Rolland 提到的更新，我进行了编辑，以便只计算一次 sqrt，哦 1 不是质数，愚蠢的我
检查素数

#include <math.h>    
bool isPrime(int n)
{
    if (n <= 1) return false;
    if (n == 2 || n == 3) return true;
    int checkRange = sqrt(n);
    for (int i = 2; i <= checkRange; i++)
    {
        if (n % i == 0)
            return false;
    }
    return true;
}

然后您将它们存储在一个集合中并使用另一个循环将其打印出来

#include <vector> //Include this - vector is a standard c++ container

//Declare in your function
std::vector<int> primes;

//In your code where you get your next fibbonacci
if (isPrime(next))
   primes.push_back(next);

//After you finished looping for fibbonacci
cout << endl << "Prime numbers are" << endl;
for (int i = 0; i < primes.size(); i++)
   cout << primes[i] << " ";

根据 OP 要求更新:完整代码，无 vector
注意: 在提取素数时，为了将它们与斐波那契分开输出，您必须将它们存储在某个地方。由于您不使用 vector ，我将使用数组来实现它。
数组的问题是，你必须用一个大小来声明它们，但你不知道在你声明它的那一刻你会得到多少素数。所以你必须声明数组的大小足以包含斐波那契数列中的所有素数

#include <iostream>
#include <math.h>
#define MAX 100
using namespace std;
bool isPrime(int n)
{
    if (n <= 1) return false;
    if (n == 2 || n == 3) return true;
    int checkRange = sqrt(n);
    for (int i = 2; i <= checkRange; i++)
    {
        if (n % i == 0)
            return false;
    }
    return true;
}
void main()
{
    int n, c, first = 0, second = 1, next, primeCount = 0;
    int primes[MAX];

    cout << "Enter the number of terms of Fibonacci series you want" << endl;
    cin >> n;

    cout << "First " << n << " terms of Fibonacci series are :- " << endl;

    for (c = 0; c < n; c++)
    {
        if (c <= 1)
            next = c;
        else
        {
            next = first + second;
            first = second;
            second = next;
        }

        cout << next << endl;

        if (isPrime(next)) //Reuse the above isPrime
        {
            primes[primeCount] = next;
            primeCount++;
        }
    }

    for (c = 0; c < primeCount; c++)
        cout << primes[c] << " ";
}