How to divide NSDecimalNumber by integer?

user_461597 0
Viewed 4403

I don't think a comprehensive, basic answer to this exists here yet, and googling didn't help.

Task: Given an NSDecimalNumber divide this by an int and return another NSDecimalNumber. Clarification: amount_text below must be converted to a NSDecimalNumber because it is a currency. The result must be a NSDecimalNumber, but I don't care what format the divisor is.

What I have so far:

// Inputs
NSString *amount_text = @"15.3";
int n = 10;

NSDecimalNumber *total = [NSDecimalNumber decimalNumberWithString:amount_text]; 

// Take int, convert to string. Take string, convert  to NSDecimalNumber.
NSString *int_string = [NSString stringWithFormat:@"%d", n];
NSDecimalNumber *divisor = [NSDecimalNumber decimalNumberWithString:int_string];
NSDecimalNumber *contribution = [total decimalNumberByDividingBy:divisor];

Surely, this can be done in a more straightforward way?

cocoa ios
4 Answers

Is there any reason why you're using NSDecimalNumber? This can be done way easier like this:

// Inputs
NSString *amount_text = @"15.3";
int n = 10;

float amount = [amount_text floatValue];
float result = amount / n;

If you really want to do it with NSDecimalNumber:

// Inputs
NSString *amount_text = @"15.3";
int n = 10;

NSDecimalNumber *total = [NSDecimalNumber decimalNumberWithString:amount_text];
NSDecimalNumber *divisor = [NSDecimalNumber decimalNumberWithMantissa:n exponent:0 isNegative:NO];
NSDecimalNumber *contribution = [total decimalNumberByDividingBy:divisor];
user_3433400

You can always use initialisers when creating NSDecimalNumber. Since it is a subclass of NSNumber, NSDecimalNumber overrides initialisers.

So you can do

NSDecimalNumber *decimalNumber = [[NSDecimalNumber alloc] initWithInt:10];

however, you should be careful if your are doing high precision calculations as there are some problems using these initialisers. You can read about it here in more detail.

user_18601340

Alternatively (potentially losing some precision):

double amount = 15.3;
double n = 10.0;
double contribution = amount / n;

// conversion to decimal
NSString *string = [NSString stringWithFormat:@"%f", n];
NSDecimalNumber *contribution_dec = [NSDecimalNumber decimalNumberWithString:string];

better yet (if n=10):

[dec decimalNumberByMultiplyingByPowerOf10:-1];
user_1951860

As per your code...

You are creating an NSDecimalNumber from string and then doing manipulations with it.

I never do that. Unless you need NSDecimalNumber unless you want a boxed Objective-C Object, Avoid it, use float and double.

If you want to do it much simpler you can do it as:

float quotient = [total floatValue]/n;

or,

float quotient = [contribution floatValue]/n;

EDIT: If you want with any specific reason to use boxed type then you can use as:

NSString *amount_text = @"15.3";
int n = 10;

NSDecimalNumber *total = [NSDecimalNumber decimalNumberWithString:amount_text];
NSDecimalNumber *divisor = [[NSDecimalNumber alloc] initWithInt:n];
NSDecimalNumber *contribution = [total decimalNumberByDividingBy:divisor];
user_13959410
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