#include using namespace std; //Function to check whether a number is prime or not. bool isPrime(int num) { if (num == 1) return false; if (num == 2 || num == 3) return true; if (num % 2 == 0 || num % 3 == 0) return false; //Multiples of prime numbers are not prime for (int i = 6; i * i <= num; i += 5) { //If number is a composite number then it must have one multiple greater(or equal) //to sqrt(num) and one multiple less(or equal) to sqrt(num). //If the num doesn't satisfy the above conditions then the number is said to be a prime number //Also prime number appear in the form of 6n-1 and 6n+1 where n is a natural number if ((num % (i - 1) == 0) || (num % (i + 1) == 0)) return false; } return true; } int main() { int num; cin >> num; //Taking input from user string result = isPrime(num) ? "Prime" : "Not Prime"; //Evaluating string based on result from isPrime function cout << result; //Printing result //Ex : num = 11 , result will print "Prime" //Time Complexity :O(sqrt(num)) return 0; }