This is a C++ prime number generator. It generates prime numbers by user specified count. It then saves the found prime numbers to a .dat file. If a user later request a lesser number of prime numbers the program will provide them from the file instead of calculating them again. The program never calculates a prime twice.

isPrime(int n) determines if a number is prime.

• Current number of saved primes are announced in the console
• The user is prompted for how many primes they want listed
• If no primes.dat exists in the program directory a primes.dat file is created
• Requested number of primes is compared to the saved number of primes in primes.dat

• If the requested is less than or equal to the number of primes saved in primes.dat the primes requested are read from primes.dat and no new calculations are preformed.
• Program then closes

• Only the additional requested primes are calculated
• The obvious cases of negative numbers, 0, 1, and all even numbers greater than 2 are eliminated.
• Modulo the test case with all odd numbers upto the square root of the test case until a 0 remainder is found or the square root of the test case is exceeded.
• true is returned if the number is prime and false is returned if the number is not prime
• If true is returned the test case is added to the vector primesFound
• In both cases of a true or false return, the function continues to the next test case until the primesFound vector contains the requested number of primes.
• Once the primesFound contains the number of user requested primes the vector primesFound is saved to the primes.dat file.