Re: How do you round a float variable in C++ - C / C++ / MFC Discussion Boards

How do you round a float variable in C++ [modified]

BlitzPackage29-Sep-06 18:48

29-Sep-06 18:48

Hello,

I have a floating point variable:

float fMyFloat;

How do I round it too a desired number of decimal places?

Thanks,
BP

-- modified at 14:38 Saturday 30th September, 2006

Re: How do you round a float variable in C++

ShilpiP29-Sep-06 19:14

ShilpiP

29-Sep-06 19:14

u use %.2f format specifier in place of %f
float fMyFloat;
printf("%.2f",fMyFloat);
Smile | :)

Re: How do you round a float variable in C++

amaneet29-Sep-06 21:42

amaneet

29-Sep-06 21:42

Sir,
I want to do the sane thing in vc++ I mean i don't want to use printf .I mean i have to round a float variable .Can i know a function that do this functionality.
Thanks

Re: How do you round a float variable in C++

ShilpiP29-Sep-06 23:14

ShilpiP

29-Sep-06 23:14

ok u may use floor function .....i m sending u one link
http://forums.dreamincode.net/showtopic8568.htm[^]
may be it will help u
Smile | :)

Re: How do you round a float variable in C++

Stephen Hewitt30-Sep-06 2:27

Stephen Hewitt

30-Sep-06 2:27

First you have to decide what kind of rounding you’re after. There are four common ways rounding can be performed:
- Towards +ve infinity.
- Towards -ve infinity.
- Towards 0.
- Away from 0.

Towards +ve infinity:
In this mode we choose the closest number that’s higher. For example, if rounding to the nearest integer:
1.6 -> 2
-1.6 -> -1

Towards -ve infinity:
In this mode we choose the closest number that’s lower. For example, if rounding to the nearest integer:
1.6 -> 1
-1.6 -> -2

Towards 0:
In this mode we chose the closet number in the direction of zero. For example, if rounding to the nearest integer:
1.6 -> 1
-1.6 -> -1

Towards 0:
In this mode we chose the closet number in the direction away from zero. For example, if rounding to the nearest integer:
1.6 -> 2
-1.6 -> -2

For simplicity I’ll only consider the “Towards +ve infinity” mode. If you want to round a double or float to the closest integer code like this will do it:
int n = double_val+0.5;

To a double to the nearest tenth:
double n = floor(double_val*10.0+0.5)/10.0;

To a double to the nearest hundredth:
double n = floor(double_val*100.0+0.5)/100.0;

Steve

Re: How do you round a float variable in C++

Hamid_RT2-Oct-06 9:02

Hamid_RT

2-Oct-06 9:02

See here[^]

WhiteSky

Re: How do you round a float variable in C++

Eytukan30-Sep-06 7:32

Eytukan

30-Sep-06 7:32

use floor and ceil

<marquee scrollamount="1" scrolldelay="1" direction="up" height="10" step="1">--[ Jig | [Dance]

]--

[My Current Status]

Link2006 wrote:Let's take it outside of CP
Jeremy : Please don't.I would love to see this.I'm making the popcorn already.

Re: How do you round a float variable in C++

BlitzPackage30-Sep-06 10:05

BlitzPackage

30-Sep-06 10:05

First, thank you all for your answers, they are proving very helpful.

Now, however, I've encountered a different issue:

I get the right results from the floor function. However, when I do the final division (I'm getting this information from stepping through the code in the VC++ .NET Debugger):

//m_fAmount is a float
m_fAmount = 30679.000
iDivisor = 1000.0000

m_fAmount / iDivisor yields: 30.679001

I am really puzzled as I'd like to think that the compiler can do simple arithmatic Smile | :)

However, in all seriousness, what's causing this, I'm really puzzled.

Any and all help is greatly appreicated.

Thanks,
BP

Re: How do you round a float variable in C++

markkuk30-Sep-06 12:52

markkuk

30-Sep-06 12:52

It's caused by round-off errors in decimal->binary->decimal conversion.

Re: How do you round a float variable in C++

BlitzPackage30-Sep-06 13:36

BlitzPackage

30-Sep-06 13:36

Do you know where I can find some information on that error and how to compensate?

Thanks,
BP

Re: How do you round a float variable in C++

Stephen Hewitt30-Sep-06 16:04

Stephen Hewitt

30-Sep-06 16:04

Just say we're working in decimal with 4 places after the decimal point. Using this scheme we can represent the following numbers exactly:
1.0000
3.0000

But it we try to divide them:
1.0000/3.0000 = 0.3333

This answer is wrong already, the correct answer us 0.333333.... (the 3 recurs forever).

So now consider this sum:
(1.0000/3.0000)*3.0000 = 0.9999

This sort of things happens in all floating or fixed point numbering systems. The computer uses base 2 and not base 10 however.

Try using double instead of float; there is seldom a good reason to prefer a float over a double

Steve

Re: How do you round a float variable in C++

BlitzPackage30-Sep-06 19:11

BlitzPackage

30-Sep-06 19:11

Thanks Steve.

Return an Object By Value

BlitzPackage29-Sep-06 17:23

BlitzPackage

29-Sep-06 17:23

Greetings Colleagues,

I have a quick question. How do you return an object by value?

The following code:

<br />
MyObject MyClass::operator+(const MyClass & mcRhs)<br />
{<br />
     //...do some processing<br />
     MyClass mcNewObject();<br />
     return mcNewObject;<br />
}<br />

results in the following error: c++ error C2664: No constructor could take the source type, or constructor overload resolution was ambiguous

It says it can't convert it. Ironically, when I leave the parentheses off of the instantiation of mcNewObject, it works!? Can someone please explain.

Thanks a million.

Sincerely,
BP

Re: Return an Object By Value

Mike_V29-Sep-06 17:36

Mike_V

29-Sep-06 17:36

Can you post the definitions of the two classes?

Or... what line was the error on?

Mike

Re: Return an Object By Value

BlitzPackage29-Sep-06 17:43

BlitzPackage

29-Sep-06 17:43

Thanks for replying,

This is the actual function

<br />
CNumber CNumber::operator+(const CNumber & cnThisNumber)<br />
{<br />
	if((m_bIsBlank) || (cnThisNumber.ReturnIsBlank()))<br />
	{<br />
		CNumber cnBlankNumber();<br />
		return cnBlankNumber;<br />
	}<br />
	else<br />
	{<br />
		float fReturnAmount;<br />
		cnThisNumber.GetAmount(fReturnAmount);<br />
		fReturnAmount = m_fAmount - fReturnAmount;<br />
		CNumber cnNewAmount(fReturnAmount);<br />
		return cnNewAmount;<br />
	}<br />
}<br />

This is the copy constructor I have defined...

<br />
CNumber::CNumber(const CNumber & cnThisNumber) : m_iMaxDecimals(10)<br />
{<br />
	// Set all changeable data to cnThisNumber<br />
	cnThisNumber.GetAmount(m_fAmount);<br />
	cnThisNumber.GetOriginalAmount(m_fOriginalAmount);<br />
	m_bFormatChange = cnThisNumber.ReturnFormatChange();<br />
	m_bIsZero = cnThisNumber.ReturnIsZero();<br />
	m_strStringAmount = cnThisNumber.ReturnStringAmount();<br />
	m_bIsBlank = cnThisNumber.ReturnIsBlank();<br />
}<br />

If I change "CNumber cnBlankNumber()" in the operator overload to "CNumber cnBlankNumber" it works. I just don't get it.

Re: Return an Object By Value

Mike_V29-Sep-06 17:59

Mike_V

29-Sep-06 17:59

I don't get the () thing, but try doing return CNumber; or return CNumber();.

Also - do you have a default constructor defined?

Mike

Re: Return an Object By Value

BlitzPackage29-Sep-06 18:04

BlitzPackage

29-Sep-06 18:04

I will try that, and yes I do have a default constructor defined.

Thanks,
BP

Re: Return an Object By Value

Anonymuos29-Sep-06 23:01

Anonymuos

29-Sep-06 23:01

BlitzPackage wrote:
It says it can't convert it. Ironically, when I leave the parentheses off of the instantiation of mcNewObject, it works!? Can someone please explain.

Because C++ is not C# or Java. Look up how you define an object in C++ using the default ctor.

Re: Return an Object By Value

bob1697230-Sep-06 5:55

bob16972

30-Sep-06 5:55

MyClass mcNewObject();

is a function declaration I think (Mike Dunn pointed that out to me via this forum when I did a similar thing a while back when trying to test constructor behavior a while back. Silly me Blush | :O

)

Finding Your Own Responses Back

Bram van Kampen29-Sep-06 16:39

Bram van Kampen

29-Sep-06 16:39

This is a 'Ping' Message just to Ensure my ID

LateNightsInNewry

Notification of unhecking the checkbox inside the DateTimeCtrl...

tamasan29-Sep-06 16:29

tamasan

29-Sep-06 16:29

Hi all,
I have a problem with DateTimepicker Control in VC6.
If I choose the DTS_SHOWNONE style how can i get a notification if the user disable the DateTimeCtrl by unchecking the small checkbox that appears inside the control.

Please help me!
Thanks a lot.

snow

Re: Notification of unhecking the checkbox inside the DateTimeCtrl...

ShilpiP29-Sep-06 19:34

ShilpiP

29-Sep-06 19:34

if we select the control style (DTS_SHOWNONE)
It is possible to have no date currently selected in the control. With this style, the control displays a check box that users can check once they have entered or selected a date. Until this check box is checked, the application will not be able to retrieve the date from the control because, in essence, the control has no date. This state can be set with the DTM_SETSYSTEMTIME message or queried with the DTM_GETSYSTEMTIME message. Smile | :)

Re: Notification of unhecking the checkbox inside the DateTimeCtrl...

Hamid_RT2-Oct-06 9:38

Hamid_RT

2-Oct-06 9:38

Im not sure its helpful for you but see here[^]

WhiteSky

Errors encountered when linking Dialog based application with C code

searcher0829-Sep-06 16:24

searcher08

29-Sep-06 16:24

I have developed a simple dialog based GUI and was attempting to link some C-code to it in the CDialog class i.e. copying the C code into the file and updating the header files. However, when I started to compile it, the following errors were encountered. I have not done anything with the MFC header files and know that it cannot be due to the program. It might be the way I inserted the c code into the GUI application. Please advise. Thanks.

c:\program files\microsoft visual studio\vc98\include\crtdbg.h(536) : error C2833: 'operator DEBUG_NEW' is not a recognized operator or type
c:\program files\microsoft visual studio\vc98\include\crtdbg.h(536) : error C2059: syntax error : 'newline'
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(674) : error C2833: 'operator DEBUG_NEW' is not a recognized operator or type
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(674) : error C2059: syntax error : 'newline'
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(674) : error C2238: unexpected token(s) preceding ';'
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(675) : error C2833: 'operator DEBUG_NEW' is not a recognized operator or type
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(675) : error C2059: syntax error : 'newline'
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(675) : error C2238: unexpected token(s) preceding ';'
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(683) : error C2833: 'operator DEBUG_NEW' is not a recognized operator or type
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(683) : error C2059: syntax error : 'newline'
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(683) : error C2238: unexpected token(s) preceding ';'
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(1631) : error C2833: 'operator DEBUG_NEW' is not a recognized operator or type
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(1631) : error C2059: syntax error : 'newline'
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(122) : error C2059: syntax error : 'string'
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(123) : error C2091: function returns function
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(123) : error C2802: static member 'operator new' has no formal parameters
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(123) : error C2333: 'new' : error in function declaration; skipping function body
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(131) : error C2059: syntax error : 'string'
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(131) : error C2091: function returns function
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(131) : error C2802: static member 'operator new' has no formal parameters
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(135) : error C2059: syntax error : 'string'
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(135) : error C2091: function returns function
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(135) : error C2556: 'void *(__cdecl *__stdcall CNoTrackObject::operator new(void))(unsigned int,const char *,int)' : overloaded function differs only by return type from 'void *(__c
decl *__stdcall CNoTrackObject::operator new(void))(unsigned int)'
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(131) : see declaration of 'new'
d:\code\jm\ldecod\inc\defines.h(22) : warning C4005: 'TRACE' : macro redefinition
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(218) : see previous definition of 'TRACE'
AVCDlg.cpp
c:\program files\microsoft visual studio\vc98\include\crtdbg.h(536) : error C2833: 'operator DEBUG_NEW' is not a recognized operator or type
c:\program files\microsoft visual studio\vc98\include\crtdbg.h(536) : error C2059: syntax error : 'newline'
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(674) : error C2833: 'operator DEBUG_NEW' is not a recognized operator or type
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(674) : error C2059: syntax error : 'newline'
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(674) : error C2238: unexpected token(s) preceding ';'
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(675) : error C2833: 'operator DEBUG_NEW' is not a recognized operator or type
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(675) : error C2059: syntax error : 'newline'
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(675) : error C2238: unexpected token(s) preceding ';'
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(683) : error C2833: 'operator DEBUG_NEW' is not a recognized operator or type
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(683) : error C2059: syntax error : 'newline'
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(683) : error C2238: unexpected token(s) preceding ';'
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(1631) : error C2833: 'operator DEBUG_NEW' is not a recognized operator or type
c:\program files\microsoft visual studio\vc98\mfc\include\afx.h(1631) : error C2059: syntax error : 'newline'
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(122) : error C2059: syntax error : 'string'
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(123) : error C2091: function returns function
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(123) : error C2802: static member 'operator new' has no formal parameters
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(123) : error C2333: 'new' : error in function declaration; skipping function body
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(131) : error C2059: syntax error : 'string'
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(131) : error C2091: function returns function
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(131) : error C2802: static member 'operator new' has no formal parameters
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(135) : error C2059: syntax error : 'string'
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(135) : error C2091: function returns function
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(135) : error C2556: 'void *(__cdecl *__stdcall CNoTrackObject::operator new(void))(unsigned int,const char *,int)' : overloaded function differs only by return type from 'void *(__c
decl *__stdcall CNoTrackObject::operator new(void))(unsigned int)'
c:\program files\microsoft visual studio\vc98\mfc\include\afxtls_.h(131) : see declaration of 'new'

OO KM

Re: Errors encountered when linking Dialog based application with C code

ShilpiP29-Sep-06 19:44

ShilpiP

29-Sep-06 19:44

plz send ur code ...what is in .cpp file and .h file ...so we encounter ur mistake

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