[C++] c pointer

• the nature of pointer

• const keyword

1. 　const int*  p
2. 　int const *p　
3. 　int*  const p
4. int const a
5. const int a

int a = 3;
int b = 5 ;
int* const p = &a;
*p =10;
//p = &b; error:  address can not be modified , but the content can be modified
const int* p2 = &a;
p2 = &b;
//*p2 = 7; error :  address can  be modified , but the content can not be modified
int const *p3 = &a;
p3 = &b;
//*p3 = 3; error :  address can  be modified , but the content can not be modified
//*p3 = 7; error