iOS Quick code question (newb)

[ryans79]

Hello!

going through my book's examples i see this bit of code:

-(IBAction)sliderChanged: (id)sender
{
UISlider *slider = (UISlider *)sender;
int progressAsInt = (int)(slider.value + 0.5f);

Works as it should, but i dont understand the last bit of

+ 0.5f

I have tested it with:
NSLog(@"slider value is: %d",(int)slider.value);

and it seems to be giving me the correct answer everytime, can someone tell me if that "+ 0.5f" is really needed? or do you use the slider the way i used it in my NSLog call?

°°

 

[Guiyon]

It's doing a cheap round operation. When typecasting a float down to an int it simply cuts off the decimal. By adding 0.5 to the value it will effectively round to the nearest integer value.

For example:
(int)(2.4 + 0.5) -> (int)(2.9) -> 2
(int)(2.6 + 0.5) -> (int)(3.1) -> 3

Also, the proper way to print the value property is

NSLog(@"slider value is: %f",slider.value);

since it is a float.

 

[ryans79]

It's doing a cheap round operation. When typecasting a float down to an int it simply cuts off the decimal. By adding 0.5 to the value it will effectively round to the nearest integer value.

For example:
(int)(2.4 + 0.5) -> (int)(2.9) -> 2
(int)(2.6 + 0.5) -> (int)(3.1) -> 3

Also, the proper way to print the value property is

NSLog(@"slider value is: %f",slider.value);

since it is a float.

Thanks!
but what if its a proper 2.0, the +0.5 will be 2.5, it kind of brings up the problem of rounding to 2 or 3, or what am i missing?

 

[Guiyon]

Thanks!
but what if its a proper 2.0, the +0.5 will be 2.5, it kind of brings up the problem of rounding to 2 or 3, or what am i missing?

Nope, no issues there. It simply truncates off everything to the right of the decimal point so 2.0 + 0.5 when typecasted to an int will be 2, which is correct.

 

[jsw]

Thanks!
but what if its a proper 2.0, the +0.5 will be 2.5, it kind of brings up the problem of rounding to 2 or 3, or what am i missing?

No, it just hacks off the stuff after the decimal point, so that 2.0 + 0.5 => 2.5, which is still just "2" after you remove anything past the decimal point. You need a value of 2.5 or higher to "round" to 3.

 

[ryans79]

Thanks again.

Since these questions are total newbie ones, i think i'll ask another without starting a separate thread,

I'm also new to the Mac and one thing is a bit puzzling, on the top left there are three dots, red, yellow/orangey and green... red is to kill the window etc, i know what they all do but sometimes the red dot has a smaller black dot/circle in it... why is that? what does it mean?

 

[Guiyon]

...but sometimes the red dot has a smaller black dot/circle in it... why is that? what does it mean?

That means there are unsaved changes in the current window.

 

[BlackWolf]

Thanks again.

Since these questions are total newbie ones, i think i'll ask another without starting a separate thread,

I'm also new to the Mac and one thing is a bit puzzling, on the top left there are three dots, red, yellow/orangey and green... red is to kill the window etc, i know what they all do but sometimes the red dot has a smaller black dot/circle in it... why is that? what does it mean?

I think that appears if the window has unsaved content ...

edit: toooo sloooow

 

[ryans79]

Ahh thanks guys!

@blackwolf, slow but still appreciated
this is all new territory for me, better more answers than less... and the same answer just confirms the first... see? my glass is half full! hehe

°°