/*
* Prime finder, starts at 2 works up, was working initially
* to 6658, now can run to 150000(highest tested yet) in ~17m25s.
* May need optimization. Uses vector size to check for nth number.
* Must have #include <vector>
*/

std::vector<int> prime;  // required for program to work.
int primes(unsigned y){
    using namespace std;
    unsigned b = 0;
    bool z = true; prime.push_back(2);
    for (b = 2; prime.size() <= y; b++){
        if (b % 2 == 0 && b < y){ b++; }//catches even numbers.
        //finds primes to the nth integer
        if (b >= 7){
                            /*decrementing in this loop produced a strange
                             *end count, used increments instead counts fixed
                             *and program completes sooner.
                             */

            for (unsigned j = 2; j < prime.size(); j++){
                //if (j > y){ return 0; }//catches infinite loop
                if (prime.at(j) >= (b/2))
                    //removes unneccessary checking
                {break;}
                if (b%prime.at(j) == 0)
                {z = false; j = prime.size();}
            }
            if (z == true){ prime.push_back(b); }
            z = true;
        }
        //inputs initial primes into array
        else if (b < 7){
            while (b <= 7){
                if (b == 2 || b == 3 || b == 5 || b == 7)
                {prime.push_back(b);} b++;
            }
        }
    }return 0;
}

int prime[] = {0};