Optimizing prime numbers code?

Question

I wrote this code to show the primes between 1 and 100. The only condition is to do not use functions, whole code should be inline. I would ask if I can improve (optimize) it mu

Answer 1

Avoid using the square root function, and increment your divisor by 2. Also some tricky things in the i loop to increment your possible prime by 2. Inner loop doesn't even need to check divisibility by 2 since no even numbers will even be tested.

int i,j,sq;
int min;
for(sq = 2; sq <= 10; sq++)
{
  min = (sq-1)*(sq-1);
  min = min + (min+1)%2; //skip if it's even, so we always start on odd
  for(i = min; i < sq*sq; i+=2)
  {
    for(j = 3; j <= sq; j+=2)
    {
      if (i%j == 0)
        bad;
    }
  }
}

note that the sq loop doesn't add time because it shrinks the inner loops proportionately.