SieveOfEratosthenes

SieveOfEratosthenesDemo.cs

using System;
using System.Collections;
using static System.Console;

int start = 1, end = 1000;
WriteLine($"The prime numbers between {start} and {end} are :");

BitArray bits = SieveOfEratosthenes(end);
for (int i = start; i <= end; i++)
{
    if (bits[i])
    {
        Write(i);
        Write(' ');
    }
}

BitArray SieveOfEratosthenes(int limit)
{
    BitArray bits = new BitArray(limit + 1, true);
    bits[0] = false;
    bits[1] = false;
    for (int i = 0; i * i <= limit; i++)
    {
        if (bits[i])
        {
            for (int j = i * i; j <= limit; j += i)
            {
                bits[j] = false;
            }
        }
    }
    return bits;
}