In C++ scope resolution operator is used to define a function outside a class. If a user  has a local variable with same name as global variable and wants to use a global variable the we use the scope resolution operator.
 

include<iostream.h>

int m=10; //(global m)

main()

{

   int m=20; //m declared local to main

{

  int K=m;

  int m=30;//m again local to inner block

  cout<<"we are in innnerbloack\n";

  cout<<"K="<<K<<"\n";

  cout<<"m="<<m<<"\n";

  cout<<"::m="<<::m<<"\n";

}

cout<<"\n we are in outerbloack \n";

cout<<"m="<<m<<"\n";}

cout<<"::m="<<::m<<"\n";

Output is

 We are in inner block

     K=20;

    m=30;

  ::m=10;

We are in outer block

    m=20;

  ::m=10;

In the above program, variable m is declared mainly at following three places:

(i) Outside the main() function

(ii) Inside the main() function

(iii) Inside the inner block.

Note: ::m will always refer to the global m.In the inner block, ::m refer to value 10 and not 20.