1、編寫函式求一系列值的平均數，引數數目不確定：

#include <stdarg.h>
double average(int n_values, ...)
{
    va_list var_arg;
    int count;
    double sum=0;

    va_start(var_arg, n_values);

    for(count=0; count<n_values; count++)
    {
        sum+=va_arg(var_arg, double);
    }
    va_end(var_arg);
    return
 
 sum/n_values;
}

int main()
{
    printf("average1=%f\n",average(5, 1.1, 2.2, 3.3, 4.4, 5.5));
    printf("average2=%f\n",average(2, 88.0, 66.6));
    return 0;
}

輸出結果為：

average1=3.300000
average2=77.300000