C++ 使用函数显示两个区间之间的质数的程序

#include <iostream>
using namespace std;
int checkPrimeNumber(int);
int main() {
    int n1, n2;
    bool flag;
    cout << "Enter two positive integers: ";
    cin >> n1 >> n2;
    // swapping n1 and n2 if n1 is greater than n2
    if (n1 > n2) {
      n2 = n1 + n2;
      n1 = n2-n1;
      n2 = n2-n1;
    }
    cout << "Prime numbers between " << n1 << " and " << n2 << " are: ";
    for(int i = n1+1; i < n2; ++i) {
        // if i is a prime number, flag will be equal to 1
        flag = checkPrimeNumber(i);
        if(flag)
            cout << i << " ";
    }
    return 0;
}
// user-defined function to check prime number
int checkPrimeNumber(int n) {
    bool isPrime = true;
    // 0 and 1 are not prime numbers
    if (n == 0 || n == 1) {
        isPrime = false;
    }
    else {
        for(int j = 2; j <= n/2; ++j) {
            if (n%j == 0) {
                isPrime = false;
                break;
            }
        }
    }
    return isPrime;
}

Enter two positive integers: 12
55
Prime numbers between 12 and 55 are: 13 17 19 23 29 31 37 41 43 47 53