Pointers

Pointers
• Every variable has a memory address. e.g.,
  int i =3, j = 5;
  double k = 6.9;
  may store the variables as:
  

  Variable	Address	Value
  i	0xF7FFF554	3
  j	0xF7FFF550	5
  k	0xF7FFF548	6.9

• In C and C++ you have access to the value and the address of a variable
• Special variables called pointers may be defined to store addresses of other variables. e.g.,
  int* p ; // Declares a pointer that will store the address of an integer variable
• The address of a variable is determined using the & operator. e.g., in the above example,
  i = 3 but &i = 0xF7FFF554
  j = 5 but &j = 0xF7FFF550
  k = 6.9 but &k = 0xF7FFF548
  
• The dereferencing operation - pointing to the value contained in an address is denoted by *
  Therefore *(&i) is equivalent to i
• Using the previous definitions of i, j, k, the following is valid:
  int* p = &i;
  and its effect is:
  

  Variable	Address	Value
  i	0xF7FFF554	3
  j	0xF7FFF550	5
  k	0xF7FFF548	6.9
  p	0xF7FFF544	0xF7FFF554

• The following statement:
  *p = 40;
  changes the above table to:
  

  Variable	Address	Value
  i	0xF7FFF554	40
  j	0xF7FFF550	5
  k	0xF7FFF548	6.9
  p	0xF7FFF544	0xF7FFF554

• Any variable that appears on the left hand side of an assignment statement is called an lvalue
  i, *p and *&i are valid lvalues
  &i is not a valid lvalue