#include <stdio.h>


void sum(int k, ...)
{
    int *p = &k;
    int sum = 0;
    for (int i = 0; i < k; ++i){
       ++p;
       sum += *p;
    }
    printf("%d", sum);
}

int main()
{
   sum(3, 1, 2, 3);
   return 0;
}

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

int sum(size_t k, ...) {
    va_list ap;
    va_start(ap, k);

    int sum = 0;

    while (k--) {
        int num = va_arg(ap, int);
        sum += num;
    }

    va_end(ap);
    return sum;
}

int main() {
   printf("%in", sum(3, 1, 2, 3));
}