/*-------------------------------------------------
    varargs.c -- use variable number of arguments
-------------------------------------------------*/

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

double sum(int, ...);

int main()
{
    double s, t;

    s = sum(3, 1.1, 2.5, 13.3);
    t = sum(6, 1.1, 2.1, 13.1, 4.1, 5.1, 6.1);

    printf("return value for sum(3, 1.1, 2.5, 13.3):                %g\n", s);
    printf("return value for sum(6, 1.1, 2.1, 13.1, 4.1, 5.1, 6.1): %g\n", t);

    return 0;
}

double sum(int lim, ...)
{
    va_list ap;                            //声明一个对象储存参数
    double tot = 0;

    va_start(ap, lim);                    //把 ap 初始化为参数列表

    for (int i = 0; i != lim; ++i)
        tot += va_arg(ap, double);        //访问参数列表的每一项

    va_end(ap);                            //清理工作

    return tot;
}