what does iostream do in c++ code example

Example 1: iostream library in cpp

// iostream_cerr.cpp
// compile with: /EHsc
#include <iostream>
#include <fstream>

using namespace std;

void TestWide( )
{
   int i = 0;
   wcout << L"Enter a number: ";
   wcin >> i;
   wcerr << L"test for wcerr" << endl;
   wclog << L"test for wclog" << endl;
}

int main( )
{
   int i = 0;
   cout << "Enter a number: ";
   cin >> i;
   cerr << "test for cerr" << endl;
   clog << "test for clog" << endl;
   TestWide( );
}

Example 2: why we use iostream in C++ programming

#include <iostream>