////////////////////////////////////////////////////////////// //***************CHALLENGE: PRIME NUMBERS SUM***************** //programm prints all pair of prime numbers whose sum equals to input //****************Author: Petros Simidyan********************* ////////////////////////////////////////////////////////////// #include #include using namespace std; inline bool isOdd(const int); vector allPrimes(const int); void printSolution(const int); 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<4) {//check, that the input is an integer cout << "Wrong input!" << endl; cout << "Your input is eather not an integer or less than 4!" << endl; cin.clear(); cin.ignore(1000, '\n'); } else { cout << "Here are all possible solutions!" << endl; printSolution(input); } } } return 0; } inline bool isOdd(const int input) { return input % 2 == 0; } //function returns vector with prime numbers vector allPrimes(const int input) { vector primVec = { 2,3 }; for (int i = 4; i <= input; i++) { for (int j = 0; ji) { primVec.push_back(i); break; } if (i%primVec[j] == 0) break; } } return primVec; } //function to print result void printSolution(const int input) { //saving all prime numbers less, or equal to input vector primVec = allPrimes(input); //if the input is a odd, we need to check all summs if (isOdd(input)) { for (int i = 0; i < primVec.size(); i++) for (int j = i; j < primVec.size(); j++) { if (primVec[i] + primVec[j] == input) cout << input << " = " << primVec[i] << " + " << primVec[j] << endl; } } //if the input is a even, we need to check only the sum with 2 //in this case is algorithm much chiper else { int i = primVec.size()-1; if (primVec[i] == input) { if (2 + primVec[i - 1] == input) cout << input << " = " << "2 + " << primVec[i - 1] << endl; } else if(primVec[i]+2==input) cout << input << " = " << "2 + " << primVec[i] << endl; } }