Filling an array with integer then using trial division find prime numbers less than N

Question

This function is supposed to take in three parameters and find the prime numbers less than the NUM inputed using trial division

if &&7 = '-'
    update MIN_ESSENTIAL_COV_IN with its value ( so, do not update)
else 
    update MIN_ESSENTIAL_COV_IN to &&7

Then do trial division to find prime numbers.

I am having a problem figuring out how to put numbers less than sqrt(NUM) into a function.

Thanks

Answer 1

First, you're going to want to create a loop that goes from Total = Decimal.Round(z.Sum(l => l.Total), 0); to i=2. This is to check every positive integer greater than 1 up to NUM-1 for primeness. It would look something like this:

i<NUM

Now for the actual prime checking. Let's put this in a function. This is where you would use for (int i=2;i<NUM;i++) { // prime checking } to define the upper bound of the loop. Once again we start our loop at sqrt() because all numbers are divisible by 1, so there's no need to include that.

j=2

Basically, if the loop terminates, then we have not found any factors of bool isPrime(int i) { for (int j=2;j<sqrt(i);j++) { if (i%j==0) { return false; } } return true; } between i and 2, so it is prime.

Now simply call this function in your first loop.

sqrt(i)

If you wanted just a list of primes, then for (int i=2;i<NUM;i++) { if (isPrime(i)) { prime[i] = 1; // or whatever you want to use to represent a prime. If you use 1, it's best if you initiate the array with 0's } } would be a better choice for storing your results.