单选题库

#include <iostream>
using namespace std;
int main() {
    int n = 17;
    bool isprime = true;
    for (int i = 2; i <= n; i++)
        if (n % i == 0)
            isprime = false;
    cout << isprime << endl;
    return 0;
}

#include <iostream>
using namespace std;
int main() {
    int cnt = 0;
    for (char ch = '1'; ch <= '9'; ch++)
        if (________) // 在此处填入代码
            cnt++;
    cout << cnt << endl;
    return 0;
}

#include <iostream>
using namespace std;
int main() {
    int a = 10, b = 50;
    ________; // 在此处填入代码
    b -= a;
    a += b;
    cout << a << " " << b << endl;
    return 0;
}