这个用c++怎么做 ，求解答

#include <iostream>
#include <stdlib.h>
#include <time.h>

using namespace std;

int main()
{
    srand((unsigned)time(NULL));
    int a = rand() % 10;
    int b = rand() % 10;
    bool flag = false;
    cout << "How much is " << a << " times " << b << "?\n";
    while (true)
    {
        if (flag)
        {
            a = rand() % 10;
            b = rand() % 10;
            cout << "How much is " << a << " times " << b << "?\n";
        }
        int res;
        cin >> res;
        if (res == a * b)
        {
            cout << "very good\n";
            flag = true;
        }
        else
        {
            cout << "No,try again\n";
            flag = false;
        }
    }
    return 0;
}

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;
int main() {
    srand(time(0));
    int a = rand() % 10, b = rand() % 10, c;
    cout << "How much is " << a << " times " << b << "?" << endl;
    while (1) {
        cin >> c;
        if (a * b != c) 
            cout << "No,try again" << endl;
        else {
            cout << "very good";
            break;
        }
    }
    return 0;
}

 
#include <iostream>
using namespace std;
int main()
{
    srand((int)time(0));
    while(1) {
        int a=rand()%10,b=rand()%10;
        while(1) {
            printf("how much is %d times %d?\n",a,b);
            int ans;
            cin>>ans;
            if(ans!=a*b) cout<<"No,try again!\n";
            else {
                cout<<"Very good!\n";
                break;
            }
        }
    }
    return 0;
}