variable arguments count in C

average.c

#include <stdio.h>
#include <stdarg.h>


double average_known_count(int, double, double, ...);
double average_zero_ended(double, double, ...);


int main(void) {
    double num1 = 16.6;
    double num2 = 13.33;
    double num3 = 66.6;
    double num4 = 133.66;

    printf("%.2lf\n", average_known_count(4, num1, num2, num3, num4));
    printf("%.2lf\n", average_zero_ended(num1, num2, num3, num4, 0.0));

    return 0;
}


double average_known_count(int count, double num1, double num2, ...) {
    va_list parg;
    double sum = num1 + num2;

    va_start(parg, num2);
    for (int i = 0; i < count-2; i++) {
        sum += va_arg(parg, double);
    }
    va_end(parg);
    return sum / count;
}


double average_zero_ended(double num1, double num2, ...) {
    va_list parg;
    int count = 2;
    double sum = num1 + num2;
    double arg;

    va_start(parg, num2);
    while ((arg = va_arg(parg, double)) != 0.0) {
        sum += arg;
        count++;
    }
    va_end(parg);
    return sum / count;
}