Problem using double in calculation

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In a simple calculation

double val = 2011.8 - 1989;

The result of val is 22.777777778 instead of 22.8. Is there any way to round this off????

Posted 28-Mar-12 23:22pm

Sumal.V

Updated 29-Mar-12 0:29am

v5

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Comments

Philippe Mori 29-Mar-12 18:22pm

For sure your example is wrong... There is far too much error in your example. It might be something like 22.799999998 which is really near but not as far as 0.022222222 off. A double has around 15 significant digits.

Sumal.V 30-Mar-12 4:06am

Well spotted! Sorry, didn't realise in a hurry. I'm glad it is solved now :)

4 solutions

Solution 1

hi
you can use the modf function:
http://www.cplusplus.com/reference/clibrary/cmath/modf/[^]

Best regards
Filipe Marques

Posted 28-Mar-12 23:26pm

Filipe Marques

Solution 2

C++

double val = 11.23;
double decimal = val - (int)val;

Posted 28-Mar-12 23:28pm

Richard MacCutchan

Comments

Sumal.V 29-Mar-12 5:50am

Uh oh!!! Yeah U r right.

But I wanted this so that I can split the decimal number, round it off to a whole number and add up with the integer, so that it would solve my problem.

float val = (2011.8 - 1989);
float decimal = ceil(val - (int)val);

But the ceil or floor rounds up the value to 0 or 1 unfortunately.

Richard MacCutchan 29-Mar-12 6:05am

Sorry, but I don't quite understand what your problem is, your description is not very clear. Please edit your original question above and try explaining exactly what problem you are trying to solve.

Sumal.V 29-Mar-12 6:30am

Hi Richard, the question is updated!

Richard MacCutchan 29-Mar-12 6:45am

You need to understand that using float/double values does not always give accurate results as the decimal part is only ever an approximation of the real number. If you want to round it for display purposes then use the appropriate format parameter in your printf() (or similar) call. If you want exact accuracy of your values then do not use floating point but stick to integers.

Sumal.V 29-Mar-12 6:54am

Yeah But I ahve to sue double/float in my calculations.

Found the solution! :)

Richard MacCutchan 29-Mar-12 6:58am

Please post your solution here so others can benefit.

Sumal.V 29-Mar-12 7:09am

Oh! yes I have accepted a solution. I hope that is enough.

Solution 4

If you want the double value as such use printf , sprintf , snprintf versions they are very fast but use format specifiers properly else it might lead to crashes.

else

you can use math.h functions if you want the round off or floor the values.

Posted 29-Mar-12 1:41am

aayushraina

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Resmi Anna · Accepted Answer · 2012-03-29T00:43:00

Solution 3

C#

#include <math.h>
:
:
double val = 2011.8 - 1989;
double roundVal = ceilf(val * 100) / 100;
</math.h>