The choice is yours fixed

#include <iostream>
#include <cstdlib>   
#include <ctime>

/**
 * In a game you may choose out of three options.
 * One of the three contains a price, the others nothing
 * After you choosed one, the moderator opens one of the others - an empty one, and asks you if you want to change your mind.
 * What would you do: keep you current choice, or take the other one.
 * 
 * You are allowed to create a program to calculate your changes :-)
 * Please do that below
 */

int main() 
{
    srand(time(nullptr));
    int N_keeper = 0;
    int N_changer= 0;

    for ( int i = 0; i < 10; ++i )
    {
        int a1 = rand() % 3;  // position of the price
        int a2 = rand() % 3;  // your choice
        int a3 = rand() % 3;  // moderator action

        while ( a3 == a1 || a3 == a2 )
        {
            a3 = rand() % 3;
        }
        std::cout("Price in "<<a1<<". Your choice is "<<a2<<". Moderator opens "<<a3<<std::endl;
        if ( a1 == a2 )
        {
            N_keeper++;
        }
        if ( a1 != a2 )
        {
            N_changer++;
        }
    }

    std::cout<<"Keeping your choice gives "<<N_keeper<<" prices out of 100"<<std::endl;
    std::cout<<"Changing your mind gives  "<<N_changer<<" prices out of 100"<<std::endl;
    return 0;
}