C语言数组下标是负数

 1 #include <iostream>
 2 #include <cstdio>
 3 using namespace std; 
 4 
 5 int main(int argc, char *argv[]) 
 6 {
 7    int a[10];
 8    int i, j, k;
 9    int *p = NULL;
10    
11    for (i=0; i<10; i++)
12        a[i] = i + 10;
13        
14    printf("Using a...\n");
15    for (i=0; i<10; i++) 
16        printf("%d ", a[i]);
17    printf("\n");
18    
19    printf("Using p...\n");
20    p= a + 1;
21    for (i=-1; i<9; i++) 
22        printf("%d ", p[i]);
23    printf("\n");
24    
25    while(1);
26    return 0;
27 }