Answer to Question #180883 in C++ for Darren

Question

1.     A positive integer n is said to be prime (or, "a prime") if and only if n is greater than 1 and is divisible only by 1 and n. For example, the integers 17 and 29 are prime, but 1 and 38 are not prime. Write a function named "is_prime" that takes a positive integer argument and returns as its value the integer 1 if the argument is prime and returns the integer 0 otherwise. Thus, for example:

         cout << is_prime(19) << endl;    // will print 1

         cout << is_prime(1) << endl;     // will print 0

        cout << is_prime(51) << endl;   // will print 0

        cout << is_prime(-13) << endl; // will print 0

Answer 1

#include <cmath>

bool is_prime(int n) {
    if (n < 1) return 0;
    const auto upperLimit = static_cast<int>(sqrtf(static_cast<float>(n)));
    auto divisors { 0 };
    for (int x = 2; x <= upperLimit; x++) {
        if (n % x == 0) divisors++;
    }
    return !divisors;
}