Adt lab/pointers

This is part of adt lab.

Pointers

In C/C++, there is a special kind of types: pointers. Pointer variables keep locations in the memory. To declare a pointer variable, we use symbol *:

type* variable;

For example, the following code declares p as a pointer to an integer.

  int* p;

To see how pointers work, let's follow this code.

  int a = 10;
  int b = 20;

  p = &a;
  cout << (*p) << endl;

  *p = 100;
  cout << a << endl;

  a++;
  cout << (*p) << endl;

  p = &b;
  a = *p;
  cout << a << endl;

Let's look at each step.

  p = &a;                   // step 1

To obtain a location of any variable, we use operator & (called a reference operator). After step 1, p keeps the location of a.

  *p = 100;                 // step 2

To dereference a pointer variable, we use operator *. Therefore *p refers to the "data" at the location that p points to. After step 2, *p (which is essentially a) becomes 100.

  a++;                      // step 3

As p points to a's location, if we change the value of a, *p also changes (because it is the "same" piece of data).

  p = &b;                   // step 4
  a = *p;

We can change p to point to other places.