Bitwise sieve

Here is an implementation of Bitwise sieve. For full explanation See this and this-

#define MAX 100000000//max num to prime
#define LMT 10000 //sqrt(MAX)

int flag[MAX/64];
int prime[100000000],total;

#define chkC(n) (flag[n>>6]&(1<<((n>>1)&31)))
#define setC(n) (flag[n>>6]|=(1<<((n>>1)&31)))

void sieve() 
{
	unsigned i,j,k;

	flag[0]|=0;
	for(i=3;i<LMT;i+=2)
		if(!chkC(i))
			for(j=i*i,k=i<<1;j<MAX;j+=k)
				setC(j);

	prime[(j=0)++] = 2;//prime starts from 0 position
	for(i=3;i<MAX;i+=2)
		if(!chkC(i))
		{
			prime[j++] = i;
			//printf("%d\n",primes[j-1]);
		}
	total = j-1;
}

Sieve of Eratosthenes (Prime Finding)

The most popular prime finding method aka Sieve of Eratosthenes.

#define MAX 35000
#define lim 200

bool a[MAX];
int prime[MAX];

void sieve()
{
	int i,j;
	a[0]=1;a[1]=1;          //1 denotes not prime

	for(i=3;i<=lim;i+=2)    //even numbers are exclusive
	{
		if(a[i]==0)     //0 denotes prime
		{
			for(j=i*i;j < MAX;j+=i)
				a[j]=1;
		}
	}

	prime[0]=2;
	j=1;
	for(i=3;i < MAX;i+=2)     //even numbers are exclusive
	{
		if(a[i]==0)
			prime[j++]=i;
	}
}