////////////////////////////////////////////////////////////// //**************** NUMBER AS ADDITION OF PRIMES ***************** //****************Author: Petros Simidyan********************* /////////////////////////////////////////////////////////////// #include #include #include using namespace std; bool isPrime(const int input)//returns true, if input is a prime { bool output = true; for (int i = 2; i*i <= input; i++) if (input%i == 0) { output = false; break; } return output; } //returns vector of prime values //needed for addition vector vecOfPrimes(const int input) { vector output; for (int i = 2; i < input ; i++) if (isPrime(i)) output.push_back(i); return output; } string printSolution(const int input) { const vector& primVec = vecOfPrimes(input); string output = ""; for (int i = 0; i < primVec.size(); i++) { for (int j = i; j < primVec.size(); j++) if (primVec[i] + primVec[j] == input) { output += to_string(input) + " = " + to_string(primVec[i]) + " + " + to_string(primVec[j]) + "\n"; } } return output; } int main() { int input; while (true) { cout << "Please give an positiv even integer number greater or equal to 4!" << endl; if (cin.peek() == '-') {//making sure, that ght input an positiv integer is cout << "The given integers should be positiv!" << endl; cin.clear(); cin.ignore(1000, '\n'); } else { cin >> input; if (cin.fail()||input%2!=0||input<4) {//check, that the input is an integer cout << "Wrong input!" << endl; cout << "Your input is eather not an integer, or not even, or less than 4!" << endl; cin.clear(); cin.ignore(1000, '\n'); } else { cout << "Here are all possible solutions!" << endl; cout << printSolution(input) << endl; } } } return 0; }

Output of a number with sum of 2 primes