va_list.c

#include <stdarg.h>
#include <stdio.h>
 
/* this function will take the number of values to average
   followed by all of the numbers to average */
double average ( int num, ... )
{
    va_list arguments;                     
    double sum = 0;
 
    /* Initializing arguments to store all values after num */
    va_start ( arguments, num );           
    /* Sum all the inputs; we still rely on the function caller to tell us how
     * many there are */
    for ( int x = 0; x < num; x++ )        
    {
        sum += va_arg ( arguments, double ); 
    }
    va_end ( arguments );                  // Cleans up the list
 
    return sum / num;                      
}
 
int main()
{
    /* this computes the average of 13.2, 22.3 and 4.5 (3 indicates the number of values to average) */
    printf( "%f\n", average ( 3, 22.2, 22.3, 4.5 ) );
    /* here it computes the average of the 5 values 3.3, 2.2, 1.1, 5.5 and 3.3 */
    printf( "%f\n", average ( 5, 5.3, 2.2, 1.1, 5.5, 3.3 ) );
}