Break from loop

Write a program that takes a user-input and finds the next prime number. Use break to stop the loop when a prime number is found.

You can refer back to task 1.5.6-1 for more information about how to find a prime number.

Example

7

11

---

500

503

Answer

#include <iostream>
#include <cmath>

int main()
{
	// Get the input from the user
	int input;
	std::cout << "Input a number to get the following prime number.\n";
	std::cin >> input;

	// This is our counter variable. 
	// It will be incremented until we find the prime number we are looking for.
	int prime_counter = input + 1; // +1 so that it doesn't start at the same number as the input
	//Infinite counting loop
	for (;; prime_counter++)
	{
		//Check if the number is prime
		bool is_prime = true;

		for (int j = 2; j <= sqrt(prime_counter); j++)
		{
			if (prime_counter % j == 0)
			{
				// If the number is not prime, update `is_prime`.
				is_prime = false;
				// Once is_prime is set to false, there's no reason to continue the inner loop, so we break from it for performance optimization.
				break;
			}
		}

		// If the number is 1 or 0, it is not prime
		if (prime_counter <= 1)
			is_prime = false;

		// If a prime number is found `prime_counter` will contain the next prime number after `input`.
		if (is_prime)
			break;
	}

	// Output the result
	std::cout << "The next prime number after " << input << " is " << prime_counter << std::endl;
}