Namespace is a new concept introduced by the ANSI C++ standards committee. For using identifiers it can be defined in the namespace scope as below.

   using namespace std;

In the above syntax "std" is the namespace where ANSI C++ standard class libraries are defined. Even own namespaces can be defined.

   namespace namespace_name
    {
      //Declaration of 
      // variables, functions, classes, etc.
    }  

#include <iostream.h>
using namespace std;
namespace Own
  {
    int a=100;
  }
int main()
  {
    cout << "Value of a is:: " << Own::a;
    return 0;
  }

   Value of a is:: 100

In the above example, a name space "Own" is used to assign a value to a variable. To get the value in the "main()" function the "::" operator is used.