Variadic function

To portably implement variadic functions in the C programming language, the standard stdarg.h header file should be used. The older varargs.h header has been deprecated in favor of stdarg.h. In C++, the header file cstdarg should be used.
To create a variadic function, an ellipsis (...) must be placed at the end of a parameter list. Inside the body of the function, a variable of type va_list must be defined. Then the macros va_start(va_list, last fixed
param), va_arg(va_list, cast type),  va_end(va_list) can be used. For example:
#include <stdarg.h>
double average(int count, ...)
{
    va_list ap;
    int j;
    double tot = 0;
    va_start(ap, count); //Requires the last fixed parameter (to get the address)
    for(j=0; j<count; j++)
        tot+=va_arg(ap, double); //Requires the type to cast to. Increments ap to the next argument.
    va_end(ap);
    return tot/count;
}