void markMultiples(bool arr[], int a, int n)
{
int i = 2, num;
while ( (num = i*a) <= n )
{
arr[ num-1 ] = 1;
++i;
}
}
void SieveOfEratosthenes(int n)
{
if (n >= 2)
{
// Create an array of size n and initialize all elements as 0
bool arr[n];
memset(arr, 0, sizeof(arr));
/* Following property is maintained in the below for loop
arr[i] == 0 means i + 1 is prime
arr[i] == 1 means i + 1 is not prime */
for (int i=1; i<n; ++i)
{
if ( arr[i] == 0 )
{
//(i+1) is prime, print it and mark its multiples
printf("%d ", i+1);
markMultiples(arr, i+1, n);
}
}
}
}