I am trying to make the operation pow(49999994,13) which results 1.220701e+100. But when i do in objective c i got the result -9223372036854775808. How can I do this operation in Objective-C correctly?
There is no pow operator in Objective-C, so use C or NSDecimalNumber (preferred).
pow
NSLog(#"%f",(double)pow(49999994,13)); // OK 12207012207044960421719...
NSLog(#"%f",(long long int)pow(49999994,13)); // WRONG -9223372036854775808
-92233... results from using a long long int instead a double.
NSDecimalNumber
As noted by Martin R, the proper way to do it in Objective-C is NSDecimalNumber, which produces as many accurate digits as possible followed by zeros.
NSDecimalNumber *n = [NSDecimalNumber decimalNumberWithString:#"49999994e0"];
n = [n decimalNumberByRaisingToPower:13];
NSLog(#"nsdecimal %#",n);
Compare the results:
accurate 12207012207044960931467189309843359073812548192494216675520514965298161665721254575494908505339305984
nsdecimal 12207012207044960931467189309843359073800000000000000000000000000000000000000000000000000000000000000
pow 12207012207044960421719677106210881027530912788496417091073101786581413645039745611250537465292783616.000000
If you see the method declaration of pow() it is something like this :
double pow(double, double);
And you saved the result into long int or you printed using integer(s) specifiers, resulting in exceeding the max limit of long int.
You can use it as :
double result=pow(49999994,13);
Related
I am trying to convert NSString to long but I am getting garbage value. Below is my code :
long t1 = [[jsonDict valueForKeyPath:#"detail.amount"]doubleValue] * 1000000000000000000;
long t2 = [[jsonDict valueForKeyPath:#"detail.fee"]doubleValue] * 10000000000000000;
NSLog(#"t1: %ld",t1);
NSLog(#"t2: %ld",t2);
detail.amout = 51.74
detail.fee = 2.72
O/P :
t1: 9223372036854775807 (Getting Garbage value here)
t2: 27200000000000000 (Working fine)
Thanks in advance.
Each number types (int, long, double, float) has limits. For your long 64 bit (because your device is 64bit) number the upper limit is :9,223,372,036,854,775,807 (see here: https://en.wikipedia.org/wiki/9,223,372,036,854,775,807)
In your case, 51.74 * 1,000,000,000,000,000,000 =
51,740,000,000,000,000,000
While Long 64bit only has a maximum of
9,223,372,036,854,775,807
So an overflow happens at 9,223,372,036,854,775,808 and above. Which is what your calculation evaluates into.
Also to note, that what you are doing will also cause problem if you only cater for 64bit long range, because what happens when your app runs on a 32bit (like iPhone 5c or below)?
Generally a bad idea to use large numbers, unless you're doing complex maths. If number accuracies are not critical, then you should consider simplifying the number like 51,740G (G = Giga). etc.
It's because you're storing the product to long type variables t1 and t2.
Use either float or double, and you'll get the correct answer.
Based on C's data types:
Long signed integer type. Capable of containing at least the
[−2,147,483,647, +2,147,483,647] range; thus, it is at least 32
bits in size.
Ref: https://en.wikipedia.org/wiki/C_data_types
9223372036854775807 is the maximum value of a 64-bit signed long. I deduce that [[jsonDict valueForKeyPath:#"detail.amount"]doubleValue] * 1000000000000000000 is larger than the maximum long value, so when you cast it to long, you get the closest value that long can represent.
As you read, it is not possible with long. Since it looks like you do finance math, you should use NSDecimalNumber instead of double to solve that problem.
In an objective C script I am trying to get a random string from an NSArray by using
int idx = rand() % self.adviceList.count;
However, every time it executes it throws an EXC_ARITHMETIC error. My question is twofold:
1) How do I get the code to run
2) is there a more portable way to generate a random int/NSUInteger in iOS programming?
The code you posted should work. Probably self.adviceList.count returns zero and this is a reason of EXC_ARITHMETIC.
As Mattt Thompson wrote in his article:
Use arc4random() and its related functions.
Specifically, to generate a random number between 0 and N - 1, use
arc4random_uniform(), which avoids modulo bias.
Try using arc4random_uniform( num ) which takes in an unsigned int
rand() returns an int and random() returns a long so it is possible modulus doesn't like unsigned numbers?
I have trouble with integer division in Dart as it gives me error: 'Breaking on exception: type 'double' is not a subtype of type 'int' of 'c'.'
Here's the following code:
int a = 500;
int b = 250;
int c;
c = a / b; // <-- Gives warning in Dart Editor, and throws an error in runtime.
As you see, I was expecting that the result should be 2, or say, even if division of 'a' or 'b' would have a result of a float/double value, it should be converted directly to integer value, instead of throwing error like that.
I have a workaround by using .round()/.ceil()/.floor(), but this won't suffice as in my program, this little operation is critical as it is called thousands of times in one game update (or you can say in requestAnimationFrame).
I have not found any other solution to this yet, any idea? Thanks.
Dart version: 1.0.0_r30798
That is because Dart uses double to represent all numbers in dart2js. You can get interesting results, if you play with that:
Code:
int a = 1;
a is int;
a is double;
Result:
true
true
Actually, it is recommended to use type num when it comes to numbers, unless you have strong reasons to make it int (in for loop, for example). If you want to keep using int, use truncating division like this:
int a = 500;
int b = 250;
int c;
c = a ~/ b;
Otherwise, I would recommend to utilize num type.
Integer division is
c = a ~/ b;
you could also use
c = (a / b).floor();
c = (a / b).ceil();
if you want to define how fractions should be handled.
Short Answer
Use c = a ~/ b.
Long Answer
According to the docs, int are numbers without a decimal point, while double are numbers with a decimal point.
Both double and int are subtypes of num.
When two integers are divided using the / operator, the result is evaluated into a double. And the c variable was initialized as an integer. There are at least two things you can do:
Use c = a ~/ b.
The ~/ operator returns an int.
Use var c;. This creates a dynamic variable that can be assigned to any type, including a double and int and String etc.
Truncating division operator
You can use the truncating division operator ~/ to get an integer result from a division operation:
4 ~/ 2; // 2 (int)
Division operator
The regular division operator / will always return a double value at runtime (see the docs):
for (var i = 4; i == 4; i = 3) {
i / 2; // 2 (double)
}
Runtime versus compile time
You might have noticed that I wrote a loop for the second example (for the regular division operator) instead of 4 / 2.
The reason for this is the following:
When an expression can be evaluated at compile time, it will be simplified at that stage and also be typed accordingly. The compiler would simply convert 4 / 2 to 2 at compile time, which is then obviously an int. The loop prevents the compiler from evaluating the expression.
As long as your division happens at runtime (i.e. with variables that cannot be predicted at compile time), the return types of the / (double) and ~/ (int) operators will be the types you will see for your expressions at runtime.
See this fun example for further reference.
Conclusion
Generally speaking, the regular division operator / always returns a double value and truncate divide can be used to get an int result instead.
Compiler optimization might, however, cause some funky results :)
NSLog(#"CEIL %f",ceil(2/3));
should return 1. However, it shows:
CEIL 0.000000
Why and how to fix that problem? I use ceil([myNSArray count]/3) and it returns 0 when array count is 2.
The same rules as C apply: 2 and 3 are ints, so 2/3 is an integer divide. Integer division truncates so 2/3 produces the integer 0. That integer 0 will then be cast to a double precision float for the call to ceil, but ceil(0) is 0.
Changing the code to:
NSLog(#"CEIL %f",ceil(2.0/3.0));
Will display the result you're expecting. Adding the decimal point causes the constants to be recognised as double precision floating point numbers (and 2.0f is how you'd type a single precision floating point number).
Maudicus' solution works because (float)2/3 casts the integer 2 to a float and C's promotion rules mean that it'll promote the denominator to floating point in order to divide a floating point number by an integer, giving a floating point result.
So, your current statement ceil([myNSArray count]/3) should be changed to either:
([myNSArray count] + 2)/3 // no floating point involved
Or:
ceil((float)[myNSArray count]/3) // arguably more explicit
2/3 evaluates to 0 unless you cast it to a float.
So, you have to be careful with your values being turned to int's before you want.
float decValue = (float) 2/3;
NSLog(#"CEIL %f",ceil(decValue));
==>
CEIL 1.000000
For you array example
float decValue = (float) [myNSArray count]/3;
NSLog(#"CEIL %f",ceil(decValue));
It probably evaluates 2 and 3 as integers (as they are, obviously), evaluates the result (which is 0), and then converts it to float or double (which is also 0.00000). The easiest way to fix it is to type either 2.0f/3, 2/3.0f, or 2.0f/3.0f, (or without "f" if you wish, whatever you like more ;) ).
Hope it helps
I created a calculator class that does basic +,-, %, * and sin, cos, tan, sqrt and other math functions.
I have all the variables of type double, everything is working fine for big numbers, so I can calculate numbers like 1.35E122, but the problem is with extremely small numbers. For example if I do calculation 1/98556321 I get 0 where I would like to get something 1.01464E-8.
Should I rewrite my code so that I only manipulate NSDecimalNumber's and if so, what do I do with sin and cos math functions that accept only double and long double values.
1/98556321
This division gives you 0 because integer division is performed here - the result is an integer part of division. The following line should give you floating point result:
1/(double)98556321
integer/integer is always an integer
So either you convert the upper or the lower number to decimal
(double)1/98556321
or
1/(double)98556321
Which explicitely convert the number to double.
Happy coding....