程序代码：

#include "stdio.h"
#include "stdlib.h"
#include "ctype.h"
int main(void)
{
    double *ptr = NULL;
    double *pstr = NULL;
    double sum = 0.0;
    int count = 0;
    int increment = 5;
    int capacity = 0;
    char answer = 'n';
    do
    {
        if (count == capacity)
        {
            capacity += increment;
            if (!(pstr = (double*)malloc(capacity*sizeof(double))))
            {
                printf("储存出错！");
                exit(1) ;
            }
            if (!ptr) ptr = pstr;
            else
            {
                for (int i = 0; i < count; i++)
                    *(pstr + i) = *(ptr + i);
                free(ptr);
                ptr = pstr;
            }
            pstr = NULL;
        }
        printf("请输入元素:");
        scanf_s("%lf", ptr + count++);
        printf("你还想要输入更多元素吗？");
        scanf_s("%c", &answer);
    } while (tolower(answer) == 'y');

    for (int i = 0; i < count; i++)
        sum += *(ptr + i);
    printf("平均数是：%.2lf.\n", sum / count);
    free(ptr);
    return 0;
}