C++ program to find primes Part C: Write a program to find, and provide a count

Question

C++ program to find primes

Part C: Write a program to find, and provide a count of prime numbers between 1 and a user provided limit or maximum value. For example, between 1 and 10,000 there are exactly 1229 prime numbers. In order to improve performance, the program should use threads to perform computations in paralle Additionally, the program should use the C++11 high resolution clock to provide an execution time in milliseconds The program should read the thread count and limit from the command line in the following format: ./primes -t -l The way to determine if a number is prime is as follows: .The numbers 2 and 3 are prime For a given number, i >3: .If i is divisible by 2, then i is not prime .If i is not divisible by 2, then: Calculate k the approximate square root of i Try to divide i by all odd numbers 3, 5, 7, etc. less than or equal to k .If i is divisible by any of these numbers, theni is not prime To estimate the square root of a number, use the following algorithm: rnumber Stop iterating when the difference between the current and previous estimates is

Explanation / Answer

#include<iostream>

using namespace std;

int main()

{

int count=0;

double sqrtEstCurr=0, number, sqrtEstPrev;

int limit;

cin >> limit;

if (limit > 0 && limit <= 2)

count = 1;

else if (limit <= 3)

count = 2;

else

{

for (int i = 4; i <= limit; i++) {

if (i % 2 != 0) {

int K = sqrt(i);

number = K;

sqrtEstPrev = sqrtEstCurr;

sqrtEstCurr = ((number / sqrtEstCurr) + sqrtEstCurr) / 2;

if (sqrtEstCurr - sqrtEstPrev < 1)

break;

for (int j = 3; j <= K; j = j + 2) {

if (i%j != 0)

count++;

}

}

}

}

cout << count << endl;

system("pause");

return 0;

}

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