I need help with a return statement from a function

[EAp4z8AR]

I am trying to return a list of mean values. Something like this:
Mean of the first 1 element(s): 1
Mean of the first 2 element(s): 3
Mean of the first 3 element(s): 4
Mean of the first 4 element(s): 5

#include <iostream>
#include <math.h>
#include <iomanip>
#include <vector>
#include <numeric>

using namespace std;

int valid(int);
vector<int> numbers;

int main()
{
    int i, x;
    
    cout << "Please enter a positive integer and '-1' to exit: ";
    cin >> i;
    
    while (i>=1)
    {
        valid(i);
        cout << "Please enter a positive integer and '-1' to exit: ";
        cin >> i;
        
        if (i == -1)
        {
            break;
            
        }
    }
    
    while (i<1)
    {
        if (i == -1)
        {
            for (x=0; x<numbers.size(); x++)
            {
                cout << "numbers[" << x << "] = " << numbers[x] << "\n";
            }
            break;
        }
        cout << "That is not a valid number! Please try again.\nPlease enter a positive integer and '-1' to exit: ";
        cin >> i;
        
        while (i>=1)
        {
            valid(i);
            cout << "Please enter a positive integer and '-1' to exit: ";
            cin >> i;
            
            if (i == -1)
            {
                for (x=0; x<numbers.size(); x++)
            {
                cout << "numbers[" << x << "] = " << numbers[x] << "\n";
            }
                break;
            }
        }
    }
}


int valid(int a)
{
    numbers.push_back(a);
    double mean = accumulate( numbers.begin(), numbers.end(), 0.0) /numbers.size();
    if (static_cast<int>(mean)==mean)
    {
        cout << "The new arithmetic mean is " << mean << "\n" << "Your input has been accepted!\n";
    }
    else
    {
        cout << "Sorry, your input was rejected and will be removed!\n";
        numbers.pop_back();
    }
}

[JLBorges]

#include <iostream>
#include <vector>

int get_int()
{
    std::cout << "Please enter a positive integer or '-1' to exit: " ;
    int n ;
    if( std::cin >> n && ( n > 0 || n == -1 ) ) return n ;

    std::cout << "invalid input. try again\n" ;
    std::cin.clear() ; // clear the (possible) failed state of std::cin
    std::cin.ignore( 1000, '\n' ) ; // throw away the rest of the input line
    return get_int() ; // and try again
}

int main()
{
    std::vector<int> numbers ;
    long long total = 0 ; // running total

    int n ;
    while( ( n = get_int() ) != -1 )
    {
        total += n ;
        numbers.push_back(n) ;

        std::cout << "mean of the " << numbers.size() << " numbers [ " ;
        for( int v : numbers ) std::cout << v << ' ' ;
        std::cout << " ] is " << double(total) / numbers.size() << '\n' ;
    }
}