C varargs: variable-length argument list

varargs.c

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

double average(int i, ...);

int main(int argc, char *argv[])
{
    double x = 22.5, y = 10.5, z = 13.2;
    printf("x+y+z=%.2f\n", average(3, x, y, z));
    printf("x+y=%.2f\n", average(2, x, y));


    return 0;
}
/**
 * @param i num of values to be averaged
 */
double average(int i, ...)
{
    double total = 0;
    va_list args;
    va_start(args, i); /* i is the rightmost arg before '...' */
    for (int j = 1; j <= i; ++j) {
        total += va_arg(args, double); // fetch next arg
    }
    va_end(args); /* clean up arg-list */
    return total;
}