Solved

[noob][c++]  cout + float + precision

Posted on 2007-11-16
10
3,357 Views
Last Modified: 2012-06-21
I am trying to do this



#include <iostream>
#include <iomanip>

//
// if I can adjust the float things then it can be used
//


using namespace std;

int main()
{
      float date;
      date = 12003932;
      cout << setprecision ( 11 ) << date << endl;
      cout << date << endl;
      cout << (date/10000) << endl;
      date = ((date/10000) + 1 ) * 10000;
      
      cout << date << endl;
      
      return 0;
      
}




this is the output




12003932
12003932
1200.3931885
12013932




for some reason this pops up


1200.3931885


when it shouldn't.


how do I fix it?
0
Comment
Question by:Troudeloup
  • 4
  • 4
  • 2
10 Comments
 
LVL 55

Accepted Solution

by:
Jaime Olivares earned 250 total points
ID: 20299471
floating numbers are not stored as decimals, indeed them are stored in inverse of the powers of 2, as explained here:
http://en.wikipedia.org/wiki/IEEE_754

So unless you control the display precision by yourself you will have thos unexpected result, try with:
cout << setprecision(4) << (date/10000) << endl;
     
0
 
LVL 84

Assisted Solution

by:ozo
ozo earned 250 total points
ID: 20300857
setprecision ( 8 )
or what do you want to happen?
0
 

Author Comment

by:Troudeloup
ID: 20300873
i just want cout to display the whole float exactly what they are.
0
Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 
LVL 55

Assisted Solution

by:Jaime Olivares
Jaime Olivares earned 250 total points
ID: 20300901
setprecision(4) will show "as you expected", but the number is really 1200.3931885
0
 
LVL 84

Assisted Solution

by:ozo
ozo earned 250 total points
ID: 20300925
The exact value, depending on your float implementation, is probably something like
1200.3931884765625
With a double, you could increase the precision to
1200.39319999999997889972291886806488037109375
0
 
LVL 84

Assisted Solution

by:ozo
ozo earned 250 total points
ID: 20300968
Or you could use int date, and get exactly
12003932
12003932
1200
12010000
0
 

Author Comment

by:Troudeloup
ID: 20300980
ok,

float a;

a = 12002323;


cout << a << endl;

should say

1.2002323e7

and

cout << a/10000 << endl;

should say

1.2002323e3





does it work simply like that?


because if the number would change unexpectedly to something else...



0
 

Author Comment

by:Troudeloup
ID: 20300989
i need to go into decimal values, so I think i can use only float
0
 
LVL 84

Assisted Solution

by:ozo
ozo earned 250 total points
ID: 20301085
<< scientific << setprecision ( 8 )
0
 

Author Comment

by:Troudeloup
ID: 20301105
nice.

can I display float like this


12003939

instead of


1.2003939


?
0

Featured Post

Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

How to remove superseded packages in windows w60 or w61 installation media (.wim) or online system to prevent unnecessary space. w60 means Windows Vista or Windows Server 2008. w61 means Windows 7 or Windows Server 2008 R2. There are various …
The purpose of this article is to demonstrate how we can use conditional statements using Python.
The viewer will learn how to pass data into a function in C++. This is one step further in using functions. Instead of only printing text onto the console, the function will be able to perform calculations with argumentents given by the user.
In a recent question (https://www.experts-exchange.com/questions/29004105/Run-AutoHotkey-script-directly-from-Notepad.html) here at Experts Exchange, a member asked how to run an AutoHotkey script (.AHK) directly from Notepad++ (aka NPP). This video…

685 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question