Необходимо переделать функцию

#include <iostream>
 #include <cstdlib>
 using namespace std;
 
 double &f(void)
 {
 static double a,b,c;
 return a;
 }
 
 int main()
 {
 
 cout << f() << ", ";
 f() = 23;
 f() = 12;
 cout << f() << ", ";
 cout << f() << ", ";
 f() = 2;
 f() = -5;
 cout << f() << '.';
 
 system("pause");
 return EXIT_SUCCESS;
 
 }

#include <iostream>
 
const double y = 3.;
const int cnt = 5;
 
double &f()
{
    static int count = cnt;
 
    static double a, b, c;
    static double mean;
 
    (--count > 3 ? a : --count > 1 ? b : c ) = (double)((int64_t)f);
    std::cout << count << '\n';
    std::cout << "a = " << a << '\n';
    std::cout << "b = " << b << '\n';
    std::cout << "c = " << c << '\n';
 
 
    return (count > 3 ? a : count > 1 ? b : count >= 0 ? c : (mean = (a + b + c)/y + (double)!(count = cnt) ));
}
 
int main()
{
    double x = 3;
    f() = x;
    x = 4;
    f() = x;
    x = 2;
    f() = x;
    std::cout << f() << '\n';
    
    return 0;
}

#include <iostream>
#include <cstdlib>
using namespace std;
 
double &f()
{
static double var1 = 0, var2 = 0, var3 = 0; 
static double var4=0;
if (var4 != var1)
{
var4=(var1+var2+var3)/3;
var3=var2;
var2=var1;
var1=var4;
}
return var1;
}
int main()
{
cout << f() << endl;
f()=23;
f()=12;
cout<<f() << endl;
cout<<f()<<endl;
f()=2;
f()=-5;
cout<<f()<<endl;
system("pause");
return EXIT_SUCCESS;
}