What is pointer and where it is used?

Answer 1

A pointer is a variable used to store a memory address. That is, we can use a pointer variable to refer to another variable (including other pointers).

Although many variables within a program have names and can be referred to directly by those names, the majority of variables are anonymous; they have no names we can refer to. For instance, every variable declared on the heap is anonymous, every element of an array is anonymous and every node in a list is anonymous. Without pointers there would be no way to refer to these anonymous variables. Moreover, there would be no way to allocate objects on the heap without pointers.

Pointers also make it possible to pass addresses into functions. In C, for instance, all arguments to a function are passed by value, however a pointer's value is a memory address thus pointers allow us to use pass by reference semantics. This makes it possible for a function to refer to an object outwith the local scope of the function.