C++ Program to Implement wheel Sieve to Generate Prime Numbers Between Given Range

Code:

#include   iostream
#include   math.h
#include   stdlib.h

using namespace std;

#define MAX_NUM 50
// array will be initialized to 0 being global
int primes[MAX_NUM];

void gen_sieve_primes(void)
{
    for (int p = 2; p < MAX_NUM; p++) // for all elements in array
    {
        if (primes[p] == 0) // it is not multiple of any other prime
            primes[p] = 1; // mark it as prime

        // mark all multiples of prime selected above as non primes
        int c = 2;
        int mul = p * c;
        for (; mul < MAX_NUM;)
        {
            primes[mul] = -1;
            c++;
            mul = p * c;
        }
    }
}

void print_all_primes()
{
    int c = 0;
    for (int i = 0; i < MAX_NUM; i++)
    {
        if (primes[i] == 1)
        {
            c++;

            if (c < 4)
            {
                switch (c)
                {
                    case 1:
                        cout << c << "st prime is: " << i << endl;
                        break;
                    case 2:
                        cout << c << "nd prime is: " << i << endl;
                        break;
                    case 3:
                        cout << c << "rd prime is: " << i << endl;
                        break;

                    default:
                        break;
                }
            }

            else
                cout << c << "th prime is: " << i << endl;
        }
    }
}

int main()
{
    gen_sieve_primes();
    print_all_primes();
    return 0;
}


Output:

1st prime is: 2
2nd prime is: 3
3rd prime is: 5
4th prime is: 7
5th prime is: 11
6th prime is: 13
7th prime is: 17
8th prime is: 19
9th prime is: 23
10th prime is: 29
11th prime is: 31
12th prime is: 37
13th prime is: 41
14th prime is: 43
15th prime is: 47



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