#include <cstdio>
#include <cstdarg>

double average_function(const int num_elements, ...)
{
    va_list elements;
    double sum = 0.0;

    va_start(elements, num_elements);
    for(int i = 0; i < num_elements; ++i) {
        sum += va_arg(elements, double);
    }
    va_end(elements);
    return sum / num_elements;
}

int main( int argc, char ** argv ) {

    printf("Average: %lf", average_function(5, 25.0, 35.7, 50.1, 127.6, 75.0));
    return 0;

}

#include <initializer_list>
#include <numeric>
#include <iostream>

double average(std::initializer_list<double> input) {
    double sum = std::accumulate(input.begin(), input.end(), 0.0);
    return sum / input.size();
}

int main() {
     std::cout << "Average: " << average({1, 2, 3, 4, 5, 6, 7, 8});
}

template<typename... Args>
double average(Args... args)
{
    return average({args...});
}