【題解】ZeroJudge a121: 質數又來囉

#include <iostream>
#include <cmath>
using namespace std;

int main() {
    int a, b, n_prime;
    bool isPrime;
    while (cin >> a >> b) {
        n_prime = 0;
        if (a <= 1)
            a = 2;
        if (b < a){
            cout << n_prime << endl;
            continue;
        }
        for (int i=a; i<=b; i++) {
            isPrime = true;
            for (int j=2; j<=sqrt(i); j++) {
                if (i % j == 0) {
                    isPrime = false;
                    break;
                }
            }
            if (isPrime)
                n_prime++;
        }
        cout << n_prime << endl;
    }
}