Which of the header file should be added in the following C++ code to properly run the program?

#include <iostream>
using namespace std;
int print_all (int num, ...)
{
    int sum = 0;
    va_list args;
    va_start (args,num);
    for (int i = 0; i < num; i++) 
    {
        int num = va_arg (args,int);
        cout<<num<<" ";
    }
    va_end (args);
    return sum;
}
int main (void)
{
    print_all(8, 1, 2, -1, 4, 12, -2, 9, 7);
    return 0;
}