float value

[diuming]

What happen? When i declare float in Xcode. please refer to attached file.

[skochan]

Floating point numbers can not always be stored exactly inside a digital computer (think about storing 1/3 or .33333333).   Search this forum, as this issue was asked once before.

Cheers,

Steve

[diuming]

Hi Steve,

thanks for your reply

In attached file content,
I declare a float data type name is floatValue that I assigned value 45.70 to it.

In my concept the result should be 45.000000
But I got the result is 45.000001 and I got the value in debug mode is 45.70000008.

So, If i got the result is 45.000001 is correct when i using NSLog or printf function?

I confuse it.

[diuming]

In my concept the result should be 45.000000
change to
In my concept the result should be 45.700000

[dharr19]

Hi,

I received the following


2011-06-30 22:20:10.217 prog4[1528:903] floatingVar = 45.700001


David

[skochan]

Yeah, once again this illustrates the fact that digital computers cannot always exactly represent a number internally.  That's the reason for that output.  When writing program examples that require comparison against floating point values, an error value, typically called epsilon, is often used.  For example, this would be the safest way to check to see if a floating point variable floatingVar contained the value 45.7:

Code: (Objective-C)

float  epsilon = .000001

if ( abs (floatingVar - 45.7) < epsilon )
   //   consider it equal to 45.7
else
   // no, it's not equal to 45.7

Cheers,

Steve