main.cpp

/*!   \mainpage Prime Numbers and Prime Twin Numbers
      \author Theodora Tataru, Student No: C00231174\n  
      \date 26 January 2020 
      \copyright  License: GNU Affero General Public License v3.0 
      \section Abstract
      \subsection _ The task is to write a parallel program that counts the number of primes less than n for any number n and also finds and lists all twin primes less than n. The code should run on linux.
*/
#include <iostream>
#include <chrono>
#include <iostream>
#include <omp.h>

/*! \fn void isPrime(int N)
    \param n The number that represents the upper limit of checking prime numbers
    \brief Method that returns if a number is prime or not
*/
bool isPrime(int n)
{
    if(n <= 1) return false;
    if(n <= 3) return true;
    if(n%2 == 0) return false;
    if(n%3 == 0) return false;
    int half = n/2;
    for(int i = 5; i<= half; i++)
    {
        if(n%i==0)
        {
            return false;
        }
    }
    return true;
}


/*! \fn void numbersPrimeLessThen(int N)
    \param N The number that represents the upper limit of checking prime numbers
    \brief Method that returns all the prime numbers less than N
*/
void numbersPrimeLessThen(int N)
{
    int count = 0;
    //#pragma omp parallel for num_threads(4) shared(count) schedule(dynamic)
    for(int number = 2; number <= N; number++) 
    {
        if(isPrime(number))
        {
            //#pragma omp atomic
            count++;
        }
    }
    printf("\nNumber of primes less than %d: %d\n", N, count);
}

/*! \fn void Primes::twins(int N)
    \param N The number that represents the upper limit of checking for prime twins
    \brief Method checks if 2 prime numbers are twins from the vector of primes
*/
void twins(int N)
{
    int sum = 0;
    //#pragma omp parallel for num_threads(4) schedule(dynamic)
    for(int i = N; i >= 2 ; i--)
    {
        if(isPrime(i) && isPrime(i+2))
        {
           // #pragma omp atomic
            sum++;
        }
    }
    printf("\nNumbers of prime twins: %d", sum);
}

/*! \fn main(int argc, char *argv[])
    \param argc Represents the number of command line arguments
    \param argv Is an array of strings (character pointers) representing the individual arguments provided on the command line
    \brief Driver method of the progran
*/
int main(int argc, char *argv[])
{
    char *numberFromCommandLine = argv[1];
    int number = atoi(numberFromCommandLine);

    auto startTime = std::chrono::high_resolution_clock::now();
    twins(number);
    numbersPrimeLessThen(number);
    auto endTime = std::chrono::high_resolution_clock::now();

    auto duration = std::chrono::duration_cast<std::chrono::microseconds>( endTime - startTime ).count();
    std::cout << std::endl;
    std::cout << "Parallel execution for N = " << number << ": " << duration << " milliseconds";

    return 0;
}