Store decimal number [closed] - ios

Question

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.
Closed 9 years ago.
I need to store a decimal number and neither a string, int or number seem to do what i want. I cannot use NSNumber because I need to be able to change it later.
I searched the whole internet but I doesn't seem to be able to find it.
The answer is probably pretty simple.
Thanks!
UPDATE:
some kind of data here
looping code{
nslog(save number);
save number 3.1415926535;
delete all data that has been stored
//now string doesn't exist anymore
}
I need to be able to save that number outside the loop in "some kind of data here" because when the loop starts over everything that is created from the loop is deleted.

Answer 1

Try using NSNumber like so:
double myValue = 20.0;
NSNumber* number = [NSNumber numberWithDouble:myValue];
// Do something with NSNumber like write it to disk, put it in an array, dictionary whatever ....
// Then pull it back out
double myOldValue = [number doubleValue];
To pull a double value out after the app has been closed (I'm interpreting that to mean "backgrounded" or "suspended"), try writing it to NSUserDefaults before the app is backgrounded and then pull it back out when your app resumes.
// Write a double to NSUserDefaults
[[NSUserDefaults standardUserDefaults] setDouble:myValue forKey:#"myDoubleValue"];
// Write an NSNumber to NSUserDefaults
[[NSUserDefaults standardUserDefaults] setObject:number forKey:#"myNumberWithDoubleValue"];
// Extract double from NSUserDefaults
double myReallyOldDoubleValue = [[NSUserDefaults standardUserDefaults] doubleForKey:#"myDoubleValue"];
// Extract NSNumber from NSUserDefaults
NSNumber* myReallyOldNumberValue = [[NSUserDefaults standardUserDefaults] objectForKey:#"myNumberWithDoubleValue"];
Or in your psuedo code:
NSNumber *someValue = [NSNumber numberWithDouble:0.0];
some kind of data here
looping code {
nslog(save number)
someValue = [NSNumber numberWithDouble:3.1412];
delete all data that has been stored
}
Store a pointer to your number or a instance variable or class property

Answer 2

You can use NSNumber, or is decimal subclass NSDecimalNumber. Just because the objects themselves are immutable doesn't mean you can't change the value a given variable points to. For example:
NSDecimalNumber *a = [NSDecimalNumber numberWithInt:2];
a = [a decimalNumberByAdding:[NSDecimalNumber numberWithInt:12]];
a = [a decimalNumberByDividing:[NSDecimalNumber numberWithDouble:2.3]];
This is just like real ints, which are also immutable.
double a = 2;
a = a + 12;
a = a / 2.3;
That being said, NSDecimalNumber is quite verbose. If you can get away with a primitive type (say, doing computations in cents instead of dollars) that might be preferable.

Answer 3

Just use a double. When it comes time to store it, you can get a number like this:
NSNumber *number = #(myDouble);
To change an NSNumber into a double,
double myDouble = [number doubleValue];