C++ Programming Code Examples
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Implement wheel Sieve to Generate Prime Numbers Between Given Range
/* Implement wheel Sieve to Generate Prime Numbers Between Given Range
This is a C++ Program to find prime number between a given range using Wheel Seive method. Wheel factorization is a graphical method for manually performing a preliminary to the Sieve of Eratosthenes that separates prime numbers from composites. Start by writing the natural numbers around circles as shown below. Prime numbers in the innermost circle have their multiples in similar positions as themselves in the other circles, forming spokes of primes and their multiples. Multiples of the prime numbers in the innermost circle form spokes of composite numbers in the outer circles. */
#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;
}
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