用于Eratosthenes筛网的C ++程序

给定数字n，请打印所有小于或等于n的素数。还假定n是一个小数。
例如，如果n为10，则输出应为“ 2、3、5、7”。如果n为20，则输出应为“ 2、3、5、7、11、13、17、19”。

C/C++

// C++ program to print all primes smaller than or equal to
// n using Sieve of Eratosthenes
#include 
using namespace std;
  
void SieveOfEratosthenes(int n)
{
    // Create a boolean array "prime[0..n]" and initialize
    // all entries it as true. A value in prime[i] will
    // finally be false if i is Not a prime, else true.
    bool prime[n+1];
    memset(prime, true, sizeof(prime));
  
    for (int p=2; p*p<=n; p++)
    {
        // If prime[p] is not changed, then it is a prime
        if (prime[p] == true)
        {
            // Update all multiples of p
            for (int i=p*2; i<=n; i += p)
                prime[i] = false;
        }
    }
  
    // Print all prime numbers
    for (int p=2; p<=n; p++)
       if (prime[p])
          cout << p << " ";
}
  
// Driver Program to test above function
int main()
{
    int n = 30;
    cout << "Following are the prime numbers smaller "
         << " than or equal to " << n << endl;
    SieveOfEratosthenes(n);
    return 0;
}
Output:Following are the prime numbers below 30
2 3 5 7 11 13 17 19 23 29Please refer complete article on Sieve of Eratosthenes for more details!Want to learn from the best curated videos and practice problems, check out the C++ Foundation Course for Basic to Advanced C++ and C++ STL Course for the language and STL.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.