C的栈为什么是向下生长的？？？

 1 #include <stdio.h>
 2 
 3 void func(int x, int y, int z)
 4 {
 5     printf("func x is %d---%p\n", x, &x);
 6     printf("func y is %d---%p\n", y, &y);
 7     printf("func z is %d---%p\n", z, &z);
 8 }
 9 
10 int main(void)
11 {
12     int x = 100;
13     int y = 200;
14     int z = 300;
15 
16     func(x, y, z);
17     printf("main x is ---%p\n", &x);
18     printf("main y is ---%p\n", &y);
19     printf("mian z is ---%p\n", &z);
20 
21     return 0;
22 }

 1 #include <stdio.h>
 2 #include <stdarg.h>
 3 
 4 int maxvalue(int n, ...)
 5 {
 6     int tmp = 0;
 7     int max = 0;
 8     int i   = 0;
 9 
10     /*定义一个指针*/
11     va_list paras; //char *paras;
12     
13     /*  根据字符串参数使指针指向第二个参数（实际的第一个参数） */
14     va_start(paras, n);
15     //paras = (char *)&n + sizeof(n); 
16 
17     while(n-- > 0)
18     {
19         /*读取向参数的值并使指针指向下一个参数*/
20         tmp = va_arg(paras, int);
21         //tmp = *(int *)(paras + (i++)*sizeof(n));  
22         max = (max > tmp) ? max:tmp;
23     }
24     /*给指针清零，防止野指针*/
25     va_end(paras);
26     //paras = NULL;
27     return max;
28 }
29 
30 int main(void)
31 {
32     int max = 0;
33 
34     max = maxvalue(3, -21, 11, -73);
35     printf("max is ---%d\n", max);
36 
37     max = maxvalue(5, 21, 11, 73, -5, 99);
38     printf("max is ---%d\n", max);
39 
40     return 0;
41 }