Answer Posted / china

Find all primes not larger than N.
I think it is the most efficient algorithm to find all
primes no larger than N.

int main(void)
{
int i,j, N;
int *pPrimes;
int nPrimes, is_prime;
printf("Input N:");
scanf("%d", &N);

pPrimes = new int [N/2];
nPrimes = 0;
for(i = 2; i<=N; i++)
{
is_prime = 1;
for(j=0;j<nPrimes; j++)
if (i%pPrimes[j] == 0)
{
is_prime = 0; break;
}
if (is_prime)
{
pPrimes[nPrimes++] = i;
}
}

printf("%d primes found less than %d:\n", nPrimes, N);
for (i=0; i< nPrimes; i++)
printf("%d ", pPrimes[i]);

}

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