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─────Run-Time Library───────────────────────────────────────────────────────
 
/* VARARG.C illustrates passing a variable number of arguments using the
 * following macros:
 *      va_start        va_arg      va_end
 *
 * Also the ANSI and UNIX type:
 *      va_list
 * and the UNIX types:
 *      va_alist        va_dcl
 */
 
/* Define symbol UNIX for UNIX version. */
#include <stdio.h>
#if !defined( UNIX )     /* ANSI-compatible version          */
#include <stdarg.h>
int average( int first, ... );
#else                    /* UNIX-compatible version          */
#include <varargs.h>
int average();           /* To avoid compiler warnings,      */
#endif                   /* don't check argument types.      */
 
void main()
{
    /* Call with 3 integers (-1 is used as terminator). */
    printf( "Average is: %d\n", average( 2, 3, 4, -1 ) );
 
    /* Call with 4 integers. */
    printf( "Average is: %d\n", average( 5, 7, 9, 11, -1 ) );
 
    /* Call with just -1 terminator. */
    printf( "Average is: %d\n", average( -1 ) );
}
 
/* Returns the average of a variable list of integers. */
#if !defined( UNIX )                /* ANSI compatible version        */
int average( int first, ... )
{
    int count = 0, sum = 0, i = first;
    va_list marker;
 
    va_start( marker, first );      /* Initialize variable arguments  */
    while( i != -1 )
    {
        sum += i;
        count++;
        i = va_arg( marker, int);
    }
    va_end( marker );               /* Reset variable arguments       */
    return( sum ? (sum / count) : 0 );
}
#else       /* UNIX-compatible version must use old-style definition. */
int average( va_alist )
va_dcl
{
    int i, count, sum;
    va_list marker;
 
    va_start( marker );             /* Initialize variable arguments  */
    for( sum = count = 0; (i = va_arg( marker, int)) != -1;  count++ )
        sum += i;
    va_end( marker );               /* Reset variable arguments       */
    return( sum ? (sum / count) : 0 );
}
#endif
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