c++ scientifc notation

[hannes]

Hi,

When i multiply 1000 by 1000, i get 1e+006. This is just scientific notation for 1.000.000 . But a million is not a very big number to write in that notation. So is there a way to get round scientif notation for not really big numbers in c++?

hannes

[Disch]

see <iomanip>

http://www.cplusplus.com/reference/iostream/manipulators/

cout << fixed << your_number;

[Cazicss]

As a side-note this code ..

cout << fixed;

will actually set a flag inside the output stream so that every other following output will not be in scientific notation.

cout << numberOne; // scientific
cout << fixed;            // set the flag
cout << numberTwo; // not in scientific
cout << numberThree << numberFour;  // not in scientific 

[Disch]

I don't think that's true.

cout << fixed << a;
is 100% identical to

cout << fixed;
cout << a;

And I recall that both of them "reset" their state after something is printed. But I could be wrong on that 2nd part (I'm positive that the above is identical though).

[Cazicss]

It is true, the flag is set and not cleared from output. Some functions like

cout << setw(2) << variable;

are in fact only usable on that one line. However fixed and scientific are flags that do not reset and are defaulted to scientific. Another multi-line setting is setprecision(). You can run this code to prove their continuity throughout multiple prints:

#include <iostream>
#include <iomanip>
using namespace std;
int main () {
  // set fixed notation and precision of 2 decimal digits
  cout << fixed << setprecision(2);

  float num1 = 1000 * 1000;
  float num2 = 2000 * 1000;
  float num3 = 3000 * 1000;
  
  cout << num1 << endl;
  cout << num2 << endl;
  cout << num3 << endl;

  // set scientific notation
  cout << scientific << endl;
  cout << num1 << endl;
  cout << num2 << endl;
  cout << num3 << endl;
  return 0;
}

[Disch]

Ah well I never really fully understood this crap. So okay. =P

My usage of iostream is extremely minimal.

[hannes]

Thanks for the help, it works.

now, i have this:

#include <sstream>
#include <iostream>

using namespace std;

int main( ) {
	ostringstream stream;
	double g1 =  1000, g2 = 1000;
	stream<<fixed;
	stream<<g1*g2;
	cout<<stream.str( );
	return 0;
}

and this is the output:

1000000.000000

It also prints out the .00000 Is there a way not to show the .00000 when it is not necessary?

hannes

[Cazicss]

In my previous example I showed

cout << fixed << setprecision(2);

In setprecision(x), the x determins how many digits to show after the decimal point. To remove all digits after the decimal point:

cout << setprecision(0);

[hannes]

I know, but sometimes a double has five digits after then dot, sometimes 1 and sometimes 0.
So is there a way a can set the precision dynamicly, not with literal integers?

hannes

[helios]

You can pass a variable to std::setprecision(), obviously.