Parsing the formatted output of C++ floating point Numbers

  • 2020-04-02 01:05:50
  • OfStack

C++ formats output floating-point Numbers

#include <iostream>
using std::cout;
using std::endl;
using std::fixed;
using std::scientific;
int main()
{
   double x = 0.001234567;
   double y = 1.946e9;
   cout << "Displayed in default format:" << endl << x << '/t' << y << endl;
   cout << "/nDisplayed in scientific format:" << endl << scientific << x << '/t' << y << endl;
   cout << "/nDisplayed in fixed format:" << endl << fixed << x << '/t' << y << endl;
   return 0;
}

Displayed in the default format:
0.00123457           1.946 e+009
Displayed in scientific format:
1.234567 e-003     1.946000 e+009
Displayed in fixed format:
0.001235               1946000000.000000

#include <iostream.h>
main(void)
{
  float a=100100.0, b=0.08;
  cout.setf(ios::right|ios::scientific|ios::showpoint);
  cout.width(20);   
  cout <<(-a*b);

  return 0;
}

8.008000 e+003

#include <iostream>
#include <iomanip>
#include <limits>
using std::cout;
using std::endl;
using std::setprecision;
using std::numeric_limits;
int main() {
  const double pi = 3.14;
  cout << endl;
  for(double radius = .2 ; radius <= 3.0 ; radius += .2)
    cout << "radius = "
    << setprecision(numeric_limits<double>::digits10 + 1)
    << std::scientific << radius<< "  area = "
         << std::setw(10) << setprecision(6)<< std::fixed << pi * radius * radi
us << endl;
  return 0;
}

The radius = 2.0000000000000001 e-001   Area =     0.125600
The radius = 4.0000000000000002 e-001   Area =     0.502400
The radius = 6.0000000000000009 e-001   Area =     1.130400
The radius = 8.0000000000000004 e-001   Area =     2.009600
The radius = 1.0000000000000000 e+000   Area =     3.140000
The radius = 1.2000000000000000 e+000   Area =     4.521600
The radius = 1.3999999999999999 e+000   Area =     6.154400
The radius = 1.5999999999999999 e+000   Area =     8.038400
The radius = 1.7999999999999998 e+000   Area =   10.173600
The radius = 1.9999999999999998 e+000   Area =   12.560000
The radius = 2.1999999999999997 e+000   Area =   15.197600
The radius = 2.3999999999999999 e+000   Area =   18.086400
The radius = 2.6000000000000001 e+000   Area =   21.226400
The radius = 2.8000000000000003 e+000   Area =   24.617600

#include <iostream>
#include <iomanip>
#include <string>
using namespace std;
int main( ) {
   ios_base::fmtflags flags = cout.flags( );
   double pi = 3.14285714;
   cout << "pi = " << setprecision(5) << pi << '/n';
   cout.flags(flags);
}

PI = 3.1429

#include <iostream>
#include <iomanip>
#include <math.h>
using namespace std;
int main()
{
   double root2 = sqrt( 2.0 );
   int places;
   cout << setiosflags( ios::fixed)
        << "Square root of 2 with precisions 0-9./n"
        << "Precision set by the "
        << "precision member function:" << endl;
   for ( places = 0; places <= 9; places++ ) {
      cout.precision( places );
      cout << root2 << '/n';
   }
   cout << "/nPrecision set by the "
        << "setprecision manipulator:/n";
   for ( places = 0; places <= 9; places++ )
      cout << setprecision( places ) << root2 << '/n';
   return 0;
}


Related articles: