//means a reference to a pointer to an int. In other words, the function can change the parameter to point to something else.
// In C, without references, the traditional way to "relocate" a pointer, is to pass a pointer to a pointer:
void c_find(int** p, int val); /* *p will point to the node with value 'val' */
//In C++, this can be expressed by the reference syntax, to avoid the awkward double dereference.
void cpp_find(int*& p, int val); // p will point to the node with value 'val'