ios - NSDecimalNumber for finances -

i'm building app deals money , i've been using floating point arithmetic until now, i've learned it's better use nsdecimalnumber.

i want make sure i've understood correctly, here goes:

imagine worker, earning 20.57$/hour. information provided user. did before:

@property (nonatomic) float hourlyrate;  nsnumberformatter *numberformatter = [[nsnumberformatter alloc] init]; numberformatter.numberstyle = nsnumberformatterdecimalstyle; nsnumber *hourlyrate = [numberformatter numberfromstring:self.ratetextfield.text]; settingsobject.hourlyrate = [hourlyrate floatvalue]; 

but i've changed to:

@property (nonatomic) nsdecimalnumber *hourlyrate;  settingsobject.hourlyrate = (nsdecimalnumber *)[nsdecimalnumber decimalnumberwithstring:self.ratetextfield.text locale:[nslocale currentlocale]]; 

is correct way read nsdecimalnumbers string?

say person enters workplace @ 10:01. save information so:

[[nsuserdefaults standarduserdefaults] setobject:[nsdate date] forkey:@"start"]; 

once person finished, start time read nsuserdefaults so:

nsdate *start = [[nsuserdefaults standarduserdefaults] objectforkey:@"start"]; 

the duration calculated so:

nstimeinterval interval = [[nsdate date] timeintervalsincedate:start] / 3600;  nsdecimalnumber *earned = [settingsobject.hourlyrate decimalnumberbymultiplyingby:[[nsdecimalnumber alloc] initwithfloat:interval]]; 

is correct , efficient way, while keeping precision?

thanks!

is correct way read nsdecimalnumbers string?

yes. however, shouldn't need cast result. should this:

settingsobject.hourlyrate = [nsdecimalnumber decimalnumberwithstring:self.ratetextfield.text locale:[nslocale currentlocale]]; 

and nslocale part isn't necessary, unless you're using non-current locale:

settingsobject.hourlyrate = [nsdecimalnumber decimalnumberwithstring:self.ratetextfield.text]; 

i don't think function likes nil values, want make sure ratetextfield has non-nil value first:

if ([self.ratetextfield hastext]) {     settingsobject.hourlyrate = [nsdecimalnumber decimalnumberwithstring:self.ratetextfield.text]; } else {     settingsobject.hourlyrate = [nsdecimalnumber zero]; } 

is correct , efficient way, while keeping precision?

yes, conversion of interval nsdecimal number , multiplication looks me.