18. Floating-point Example

• 
      #include <iostream>
      using namespace std;
      int main()
      {
          const double PI = 3.1415926;
          cout.precision( 7 );
          cout << fixed << "fixed format: " << PI << '\n';
          cout << scientific << "scientific format: " << PI << '\n';
          // back to default format:
          cout.unsetf( ios_base::fixed );
          cout.unsetf( ios_base::scientific );
          cout << "default format: " << PI << '\n';
          return 0;
      }
      /*
      Output:
      fixed format: 3.1415926
      scientific format: 3.1415926e+000
      default format: 3.141593
      */