cpp/CPrimerPlus6E/Ch16/varargs.c

//varargs.c -- use variable number of arguments
#include <stdio.h>
#include <stdarg.h>
double sum(int, ...);

int main(void)
{
    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;                    // declare object to hold arguments
    double tot = 0;
    int i;
    
    va_start(ap, lim);             // initialize ap to argument list
    for (i = 0; i < lim; i++)
        tot += va_arg(ap, double); // access each item in argument list
    va_end(ap);                    // clean up
    
    return tot;
}