The code I wrote is more interactive this time as it allows you specify the number of primes you want. Be careful; though this is relatively fast, if you input a really large number, you may have to leave your computer running for a couple hours.
The code is as below:
#include <iostream>
#include <list>
using namespace std;
int main (int argc, char * const argv[]) {
// Number of primes the user will specify
int numberOfPrimes;
// STL container that dynamically stores all the prime numbers.
list primes;
// An iterator for loopint through this container.
list::iterator primeIterator;
// This is the little trick. I know the first prime number is 2,
// so that is injected into the list
primes.push_back(2);
// Request for the number of primes.
cout << "Enter number of primes you want: ";
cin >> numberOfPrimes;
/* RUNTIME GUARD */
// if (numberOfPrimes > 999) {
// cout << "Number is too large" << endl;
// return 0;
// }
/* Computation Loop
* This is where all compoputation is done.
*
* To do the wor are a couple new actors.
* Introducing the cast, we have:
* i -> keeps count of the number of primes and makes
* sure the user gets his required number.
* j -> presents numbers to be processed for 'prime'ness
* isPrime -> gets high when a 'j' is prime
* (This does not refer to hitting Js and getting high.
* I meant it in the most programming terms possible).
*/
for (int i = 0, j = 2; i < numberOfPrimes - 1; ++j) {
bool isPrime = true;
for (primeIterator = primes.begin();
primeIterator != primes.end(); ++primeIterator) {
if (j % (*primeIterator) == 0)
isPrime = false;
}
if (isPrime) {
// Add the number to the primes collection
primes.push_back(j);
++i;
}
}
// Print out the Nth prime number.
primeIterator = primes.end();
--primeIterator;
cout << *primeIterator << endl;
return 0;
}
