Constant pointer vs Pointer to constant [duplicate]

Answer 1

const int* ptr;

is a pointer to constant (content). You are allowed to modify the pointer. e.g. ptr = NULL, ptr++, but modification of the content is not possible.

int * const ptr;

Is a constant pointer. The opposite is possible. You are not allowed to modify the pointer, but you are allowed to modify what it points to e.g. *ptr += 5.