C++ question(Decimal places)very weird

[maherddd]

this is an example of what is happening

consider the program:

#include

void main(void)
{

double x=2.3767553235;
cout<

[maherddd]

so my point is i want 2.3767553235 in the output,why is the pc only putting 2.37676

[Dogtree]

>> Why?
Why not? It's concievable that there would be a default precision for the stream, one that would be valid everywhere so that it could be portable. It just so happens that that's the case. The default is 6:

#include <iostream>

int main()
{
  double d = 123.4567890123;

  std::cout << "Precision: " << std::cout.precision() << '\n';
  std::cout << "Value: " << d << '\n';
  std::cout.precision(4);
  std::cout << "Value: " << d << '\n';
}

>> i want it to be say for example 8 or 10 decimal places
Assuming your system is capable of holding an accurate precision to 10 digits past the radix including an arbitrary number of digits before the radix, you would do it like this:

#include <iostream>

int main()
{
  double x = 2.3767553235;

  std::cout.precision(11);
  std::cout << x << '\n';
}

However, because the precision isall digits in the number, to get an exact precision of 10 for any whole value, you would need a way to determine the number of digits before the radix. An easy to understand solution is to make a string and take its length:

#include <iostream>
#include <sstream>

namespace jrd {
  int digits(double val)
  {
    std::ostringstream oss;

    oss << static_cast<int>(val);

    return oss.str().length();
  }
}

int main()
{
  double x = 2.3767553235;

  std::cout.precision(10 + jrd::digits(x));
  std::cout << x << '\n';
}

[maherddd]

whats the difference between and ?

[Dogtree]

is not standard, and therefore is becoming increasingly less supported by compilers as standard C++ matures. This isn't a theoretical difference, by the way. My compiler will refuse to compile .

[little nell]

Another important difference between iostream.h and iostream is that iostream.h has its declarations in the global namespace, while iostream has them in the std namespace.

dogtree's method is quite inefficient. It is possible to directly set the number of decimal places, but you have to make sure the output mode is "fixed" first.

This example produces 10 decimal places.

#include<iostream>

using namespace std;

int main()
{
	double x = 2.3767553235;
	cout << fixed << showpoint << setprecision(10) << x << endl;
}

If you google for "C++ decimal places" you will find this article http://www.cs.fsu.edu/~myers/c++/notes/basics1.html

and right at the end is a short explanation of formatting decimal numbers.

[Dogtree]

You need to include for setprecision().