using namespace in program block : namespace « Language Basics « C++ Tutorial

1. C++ Tutorial
2. Language Basics
3. namespace

#include <iostream.h>

namespace first
{
  int var = 5;
}

namespace second
{
  double var = 3.1416;
}

int main () {
  {
    using namespace first;
    cout << var << endl;
  }
  {
    using namespace second;
    cout << var << endl;
  }
  return 0;
}

5
3.1416