To be tested...

console.cpp

#include <iostream>
#include <iomanip>

//using namespace std;

void display(double n)
{
  std::cout << "Flottant :  \"" << n << "\"  (précision " << std::cout.precision() << ")" << std::endl;
}

void display(long n)
{
  //std::cout << "Entier   :  \"" << n << "\"  (largeur " << std::cout.width() << ")" << std::endl;
  std::cout << n << std::endl;
}

void process(double n)
{
  using namespace std;

  cout << "n = " << setfill('#') << setprecision(1) << n << endl;
  cout << "n = " << setfill('#') << setprecision(3) << n << endl;
  cout << "n = " << setfill('#') << setprecision(7) << n << endl;
  cout << "n = " << setfill('#') << setprecision(15) << n << endl;
  cout << "n = " << setfill('#') << setprecision(25) << n << endl;

  cout << endl;

  std::cout << std::fixed;

  cout << "n = " << setfill('#') << setprecision(1) << n << endl;
  cout << "n = " << setfill('#') << setprecision(3) << n << endl;
  cout << "n = " << setfill('#') << setprecision(7) << n << endl;
  cout << "n = " << setfill('#') << setprecision(15) << n << endl;
  cout << "n = " << setfill('#') << setprecision(25) << n << endl;

  cout << endl;

  std::cout << std::scientific;

  cout << "n = " << setfill('#') << setprecision(1) << n << endl;
  cout << "n = " << setfill('#') << setprecision(3) << n << endl;
  cout << "n = " << setfill('#') << setprecision(7) << n << endl;
  cout << "n = " << setfill('#') << setprecision(15) << n << endl;
  cout << "n = " << setfill('#') << setprecision(25) << n << endl;

  cout << endl;

  return;

  std::cout << std::setprecision(0);
  display(n);

  std::cout << std::setprecision(1);
  display(n);

  std::cout << std::setprecision(2);
  display(n);

  std::cout << std::setprecision(3);
  display(n);

  std::cout << std::setprecision(4);
  display(n);

  std::cout << std::setprecision(5);
  display(n);

  std::cout << std::setprecision(10);
  display(n);
}

void process(long n)
{
  using namespace std;

  std::cout << std::left;
  cout << "n = " << setfill('*') << setw(3) << n << endl;
  std::cout << std::internal;
  cout << "n = " << setfill('#') << setw(3) << n << endl;
  std::cout << std::right;
  cout << "n = " << setfill('#') << setw(3) << n << endl;

  std::cout << std::left;
  cout << "n = " << setfill('*') << setw(15) << n << endl;
  std::cout << std::internal;
  cout << "n = " << setfill('#') << setw(15) << n << endl;
  std::cout << std::right;
  cout << "n = " << setfill('#') << setw(15) << n << endl;

  n = -n;

  std::cout << std::left;
  cout << "n = " << setfill('*') << setw(15) << n << endl;
  std::cout << std::internal;
  cout << "n = " << setfill('#') << setw(15) << n << endl;
  std::cout << std::right;
  cout << "n = " << setfill('#') << setw(15) << n << endl;

  return;

  std::cout << std::left;
  //std::cout << std::internal;

  display(n);

  std::cout << std::setfill('#');

  display(n);

  std::cout << std::setw(2);
  display(n);

  std::cout << std::right;
  display(n);

  std::cout << std::setw(10);
  display(n);
}

int main()
{
  long   i = 27523;
  double f = -3.14159265359;

  //process(i);
  process(f);

  return 0;
}