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1, C++ program: input a positive integer, output in reverse order.

#include 
using namespace std;

int main() {
    int num, reverse = 0;

    cout << "请输入一个正整数：";
    cin >> num;

    while(num > 0) {
        int digit = num % 10;
        reverse = reverse * 10 + digit;
        num /= 10;
    }

    cout << "倒序输出为：" << reverse << endl;

    return 0;
}

2, C++ program: input a positive integer N, output from 2 to N all the prime sum.

#include 
using namespace std;

bool isPrime(int num) {
    if(num == 1) {
        return false;
    }
    for(int i = 2; i <= num/2; i++) {
        if(num % i == 0) {
            return false;
        }
    }
    return true;
}

int main() {
    int n;
    int sum = 0;

    cout << "请输入一个正整数：";
    cin >> n;

    for(int i = 2; i <= n; i++) {
        if(isPrime(i)) {
            sum += i;
        }
    }

    cout << "2到" << n << "的素数和为：" << sum << endl;

    return 0;
}

In the above code, the isPrime function is used to determine whether a number is prime, returning true if it is prime, false otherwise. In the main function, we use a loop to determine in turn whether all the numbers from 2 to N are prime, and if so, add them to sum. Finally output the result.