STATIC_ CLASS_ MEMBERS, MACROS-CONST-INLINEFUNCTIONS, REFERENCE_ VARIABLES-AND- PASS_BY_REFERENCE

 Static class members:
  a) We can create class members[common for all objects] using the keyword static.
b) We can access the static members using :: (scope resolution operator), without an object.
c) Static members need to be redefined outside the class.
d) Static functions can access only static data members.

class A
{
public:
static int x;
static void stat_function();
};
int A::x = 0;
void A::stat_function()
{
cout<<x<<endl;
}

Macros, Const and Inline functions:
Macro:
#define A 10

Whenever we use 'A', it is replaced with the value 10.

Macros are just replaced.

Const:
const int A = 1;

a) The value of a constant member cannot be changed.
b) If we declare a function as constant, we cannot change the values inside that.
c) If we declare a class as 'const', we cannot change its values, except mutable members.

Inline functions: (the statements are added in the call)
a) Inline functions cannot have complex operations.
b) The inline keyword is a request to the compiler, 
the compiler may replace the statements in the called function or it can treat the inline function as a normal one.

Reference variables and pass by Reference:
Reference -> giving an alias name to the same variable.

e.g.
int a;
int &ref = a;
a = 1;

Reference variable needs to be initialized at the time of declaration.

Pass by Reference:
  a) variables can be passed to other functions as pass by reference.
b) It doesn't create a copy of a variable, instead it refers the same memory location.

e.g.
void PassByReference(int &x, int &y)
{
x = x + 10;
y = y + 10;
}

calling Function:
int x=1, y=1;
PassByReference(x, y);

The changes made in the function is reflected in the calling function also.