无法通过指针访问数组值

Question

int *ptrr;
int array[3];
for(int i=3;i>0;--i){
      array[i]=i*100;cout<<array[i]<<" "<< & array[i]<<endl;
}
ptrr=array;
for(int i=3;i>0;--i){
    cout<<*(ptrr+i)<<" ";
}
cout<<endl;
for(int i=3;i>0;--i){
    cout<<ptrr[i]<<" ";
}
cout<<endl;
cout<<ptrr<<" "<<*ptrr<<" "<<*ptrr+1<<*ptrr+2<<endl;

I have a basic question that I am able to access the array elements through a pointer in a loop, but when accessed separately it pops out weird values. The pointer is same still giving different values. What is the problem..?

Output:

300 0x7ffface5538c
200 0x7ffface55388
100 0x7ffface55384
300 200 100 
300 200 100 
0x7ffface55380 -1394257008 -1394257007 -1394257006

Answer 1

Use *(ptrr+1) and *(ptrr+2) . * has higher priority than + .

Answer 2

You have two different issues in your code.

First your loop iterator is wrong. Your array is of size 3 (valid indices are 0, 1, 2), so there is no array[3] (this memory location is out of scope).

you should rewrite your loops like given below

for(int i=2;i>=0;--i){
      array[i]=i*100;cout<<array[i]<<" "<< & array[i]<<endl;
}

Secondly you should use () in below statement.

cout<<ptrr<<" "<<*ptrr<<" "<<*ptrr+1<<*ptrr+2<<endl;

and rewrite your statement as

cout<<ptrr <<" "<<*ptrr<<" "<<*(ptrr+1)<< " " << *(ptrr+2)<<endl;

The syntax *ptrr is perfectly fine but since you had started your loop from i=3 and terminated at i>0 (ie i=1) so array[0] remained uninitialized and garbage value was assigned. But with the initialization in my answer it will work.