Prime numbers

What is the Prime Number?

A prime number is a special natural number. It has exactly two divisors – 1 and itself.

How to find a prime number?

• Take the root of the number to be examined
• Note which prime numbers exist so far
• Apply these prime numbers to the original number and see if they divide without a remainder.
• If no number is found until then, it is a prime number.

Output of Prime Numbers

#include <iostream>
using namespace std;

int primeAlgorithm(unsigned int number) {
    int counter = 0;

    for (int i = 1; i <= number ; i++) {
        if (number % i == 0) {
            counter += 1;
        }
    }

    if (counter == 2) {
        return number;
    } else {
        return 0;
    }
}

int main() {
    unsigned int number;

    cout << "Enter upper limit of prime numbers: ";
    cin >> number;

    for (int i = 1; i <= number; i++) {
        if (primeAlgorithm(i)) {
            cout << primeAlgorithm(i) << endl;
        }
    }
}

Output

Enter upper limit of prime numbers: 50
2
3
5
7
11
13
17
19
23
29
31
37
41
43
47

Check if number is Prime Number

#include <iostream>
using namespace std;

bool isPrime(unsigned int number) {
    if (number <= 1)  return false;

    for (int i = 2; i <= number / 2 ; ++i) {
        if (number % i == 0) {
            return false;
        }
    }

    return true;
}

int main() {
    unsigned int number;

    cout << "Enter a number to check whether it is a prime number: ";
    cin >> number;

    if (isPrime(number)) {
        cout << number << " is a prime number!" << endl;
    } else {
        cout << number << " is not a prime number!" << endl;
    }
}

Output

Enter a number to check whether it is a prime number: 13
13 is a prime number!