This question already has an answer here:
How to convert NSNumber objects for computational purposes?
(1 answer)
Closed 9 years ago.
I have an array:
SomeArray =[[NSMutableArray alloc]initWithObjects:[NSNumber numberWithFloat:50.0],[NSNumber numberWithFloat:120.0],[NSNumber numberWithFloat:200.0],nil];
When I retrieve it:
NSNumber* Target = [SomeArray objectAtIndex:0];
When I NSLog it:
NSLog(#"Target %d",Target);
it return something funky like
2013-06-26 01:47:58.940 KKK[1027:c07] Target 121016880
What is the proper way to do this?? I just need the number in the array to be used as float.
You are retrieving a NSNumber, which is an object.
%d is for logging decimals, which is not your case.
Either you log it with
NSLog(#"Target %#", target);
or you convert it to a float and use %f
NSLog(#"Target %f", [target floatValue]);
And PLEASE don't use capitalized identifiers for variables!
You are asking for a decimal %d in the log and also a primitive type. NSNumber is an object that wraps a primitive type numbers. So you can do like that
NSLog(#"target %f",[Target floatValue]) or NSLog(#"target %#",Target). With the first you are sending a message to the object to unwrap the float value with the latter you are asking for the object description that in this case is the number
Related
So I have the following in an Xcode 6.3 project where I have _menuHeaderPositions which should hold a keys of a menuHeaderID and an NSNumber which represents the contentOffset:
// _menuHeaderPositions is a NSMutableDictionary
// should be a NSNumber created from an NSUInteger
[_menuHeaderPositions setObject:[NSNumber numberWithFloat:_runningYPosition] forKey:[NSNumber numberWithInteger:menuHeader.menuHeaderID]];
// so unsigned long because of complaints about int
firstButton.tag=(unsigned long)menuHeaderID;
... later firstButton -> thisTap.view
// Works Fine
NSLog(#"you tapped me %lu", [_menuHeaderPositions objectForKey:[NSNumber numberWithInteger: thisTap.view.tag]]);
// THIS IS THE ISSUE
// Implicit Conversion loses integer precision: 'NSInteger' (aka long) to 'int'
NSNumber *pos=[_menuHeaderPositions objectForKey:[NSNumber numberWithInt:thisTap.view.tag]];
But I get this error and am pretty clueless as to what is going on here:
Implicit Conversion loses integer precision: 'NSInteger' (aka long) to 'int'
I can access the correct value later as [pos floatValue] but how do I get this warning to go away?
edit 1
trying this didn't seem to work:
NSNumber *pos=[_menuHeaderPositions objectForKey:[NSNumber numberWithInt:#(thisTap.view.tag)]];
The tag property has a type of NSInteger. You are attempting to pass this NSInteger to a method (numberWithInt:) that expects an int.
You have two choices:
Use NSNumber numberWithInteger:
NSNumber *pos=[_menuHeaderPositions objectForKey:[NSNumber numberWithInteger:thisTap.view.tag]];
Use modern boxing: #(thisTap.view.tag)
NSNumber *pos=[_menuHeaderPositions objectForKey:#(thisTap.view.tag)];
You can also use modern dictionary syntax and the line simply becomes:
NSNumber *pos = _menuHeaderPositions[#(thisTap.view.tag)];
First you should clear the data type of your menuHeader.menuHeaderID, which has two identity —— the key of the dictionary and the tag of the view.
As #rmaddy said, the tag property of the UIButton has type of NSInteger, which is NOT simply int.
This is the doc of numberWithInt: and numberWithInteger:.
Briefly speaking, use numberWithInteger: rather than numberWithInt:.
firstButton.tag = (NSInteger)menuHeaderID;
NSNumber *pos = [_menuHeaderPositions objectForKey:[NSNumber numberWithInteger:thisTap.view.tag]];
This question already has answers here:
How to convert an NSString into an NSNumber
(18 answers)
Closed 8 years ago.
I've tried to convert the UITextfield Value Into a float first then convert it to an NSNumber but that doesn't seem to work as seen below.
float carb = [self.carbGrams.text floatValue];
NSLog(#"%.2f", carb);
nCarbGrams = carb;
In the last line I get this error message:
Assigning to 'NSNumber *__strong' from incompatible type 'float'
I've then just tried assigning carb as an NSNumber by doing this
NSNumber *carb = [self.carbGrams.text floatValue];
NSLog(#"%.2f", carb);
nCarbGrams = carb;
But I get this error message instead :
Initializing 'NSNumber *__strong' with an expression of incompatible type 'float'
As I've read I though NSNumber could accept any type of numeric value but I seem to be incorrect, can someone please evaluate the problem?
You can use Objective-C literal syntax:
NSNumber *carb = #([self.carbGrams.text floatValue]);
You need to create an object of typ NSNumber from the float. As such
float carb = [self.carbGrams.text floatValue];
NSNumber *nCarb = [NSNumber numberWithFloat: carb];
or why not use the fancy (new) literal syntax
NSNumber *nCarb = #([self.carbGrams.text floatValue]);
Try this:
NSNumber *carb = [NSNumber numberWithFloat:[self.carbGrams.text floatValue]];
This question already has answers here:
Objective C Issue With Rounding Float
(4 answers)
Closed 9 years ago.
The APP I'm writting must do some financial calculations, basically it's all about credits, debits and the balance. The only problem (so far) is that if I calculate 999999999.99 - 0.00 the result is 1000000000.00. Please, does anyone know why that happens? Here's my code:
NSNumber *totalCredits;
NSNumber *totalDebits;
NSNumber *balance;
self.credits = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
totalCredits = [self.credits valueForKeyPath:#"#sum.amount"];
double totalCreditsDouble = [totalCredits doubleValue];
self.creditLabel.text = [NSString stringWithFormat:#"%1.2f", totalCreditsDouble];
self.debits = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
totalDebits = [self.debits valueForKeyPath:#"#sum.amount"];
double totalDebitsDouble = [totalDebits doubleValue];
self.debitLabel.text = [NSString stringWithFormat:#"%1.2f", totalDebitsDouble];
balance = [NSNumber numberWithFloat:([totalCredits floatValue] - [totalDebits floatValue])];
double balanceDouble = [balance doubleValue];
self.balanceLabel.text = [NSString stringWithFormat:#"%1.2f", balanceDouble];
All the data is stored as Double.
The C type double is generally not very well suited for financial calculations.
Foundation.framework has a good data type for that: NSDecimalNumber. NSDecimalNumber uses a decimal representation and has 36 digits of precision.
http://floating-point-gui.de/ is a good resource to start with. You are trying to store exact values using a datatype which cannot represent them with the accuracy or precision you need.
if the integrity of these calculations is important to you then you need to switch to storing these values in a format which accurately represents them.
In this case a simple solution might be to store all of your currencies in their smallest possible denomination (e.g. cents) as integers (assuming you don't need fractional cents and handle any division carefully and consistently).
This question already has answers here:
Convert to Float and Calculate
(3 answers)
What is a fast C or Objective-C math parser? [closed]
(4 answers)
Closed 9 years ago.
I want to convert a string for example
NSString *stringWithNumber = #"3/4"
into a NSNumber.
How is this possible?
You can use an NSEXpression to "calculate" the value. Note that you will have the regular int division problem with "3/4".
NSExpression *expression = [NSExpression expressionWithFormat:#"3.0/4.0"];
NSNumber *result = [expression expressionValueWithObject:nil context:nil];
If you are only working with n/m fractions, and you mean to have a number representing the result of the fraction, you can do something like
NSString *fraction = #"3/4";
NSArray *components = [fraction componentsSeparatedByString:#"/"];
float numerator = [components[0] floatValue];
float denominator = [components[1] floatValue];
NSNumber *result = #(numerator/denominator);
NSLog(#"%#", result); // => 0.75
Of course this can easily break in case of malformed strings, so you may want to check the format before performing the above computation.
NOTE
In case the fractions coming in input have a format compatible with native float division, David's answer is definitely sleeker and less clunky than mine. Although if you have an input like #"3/4", it won't work as expected and you definitely need to do something like I suggested above.
Bottom line, you should specify better your requirements.
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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.
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
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.
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];