I have a method that receives a number in a NSString format.
I wish to convert this string to a double which I can use to calculate a temperature.
Here's my method.
NSString *stringTemp = text; // text is a NSString
NSLog(#"%#",stringTemp); // used for debugging
double tempDouble = [stringTemp doubleValue];
NSLog(#"%f",tempDouble); // used for debugging
Please note I put the NSLog commands here just to see if the number was correct. The latter NSLog returns a value of 82.000000 etc. (constantly changes as it's a temperature).
Next I wanted to use this double and convert it to a Celsius value. To do so, I did this:
double celsiusTemp = (5 / 9) * (tempDouble - 32);
Doing this: NSLog(#"%d", celsiusTemp); , or this: NSLog(#"%f", celsiusTemp); both give me a value of 0 in the console. Is there any reason why this would be happening? Have I made a stupid mistake somewhere?
Thank you for your help!
Try doing (5.0 / 9.0). If you only use an int to do math where you are expecting a double to be returned (like 0.55) everything after the decimal place will be lost because the cpu expects an int to be returned.
5 / 9 is the division of two integers, and as such uses integer division, which performs the division normally and then truncates the result. So the result of 5 / 9 is always the integer 0.
Try:
double celsiusTemp = (5.0 / 9) * (tempDouble - 32);
If you evaulate (5/9) as an integer, then it is just 0.
Related
I'm trying to do basic division and it always returns 0 as an answer.
let mathStuff = Double((stepCount / Level.expRequired())) * 100
print ("\(totalSteps) / \(Level.expRequired()) * 100 = \(mathStuff)")
My print returns
2117 / 2500 * 100 = 0.0
I've tried using NSDecimal instead of a Double and have also tried not using Double or NSDecimal and having it just do the math, which comes back as 0 instead of 0.0.
I'm really confused on what I'm doing wrong here, this seems like basic math and I'm not sure why I'm always given 0 as an answer.
Your problem probably lies here: 2117 /2500, both 2500 and 2117 are Ints.
If they were Double, then it would work: 2117.0 /2500.0 ==> produces non-zero division
Try casting those variables to double first, and you don't need to cast the result itself:
Double(stepCount) /Double(Level.expRequired()))*100
In fact, I believe only one needs to be cast:
Double(stepCount)/Level.expRequired())*100
In a cocos2d game, I use arc4random to generate random numbers like this:
float x = (arc4random()%10 - 5)*delta;
(delta is the time between updates in the scheduled update method)
NSLog(#"x: %f", x);
I have been checking them like that.
Most of the numbers that I get are like this:
2012-12-29 15:37:18.206 Jumpy[1924:907] x: 0.033444
or
2012-12-29 15:37:18.247 Jumpy[1924:907] x: 0.033369
But for some reason I get numbers like this sometimes:
2012-12-29 15:37:18.244 Jumpy[1924:907] x: 71658664.000000
Edit: Delta is almost always:
2012-12-29 17:01:26.612 Jumpy[2059:907] delta: 0.016590
I thought it should return numbers in a range of -5 to 5 (multiplied by some small number). Why I am getting numbers like this?
arc4random returns a u_int32_t. The u_ part tells you that it's unsigned. So all of the operators inside the parentheses use unsigned arithmetic.
If you perform the subtraction 2 - 5 using unsigned 32-bit arithmetic, you get 232 + 2 - 5 = 232 - 3 = 4294967293 (a “huge number”).
Cast to a signed type before performing the subtraction. Also, prefer arc4random_uniform if your deployment target is iOS 4.3 or later:
float x = ((int)arc4random_uniform(10) - 5) * delta;
If you want the range to include -5 and 5, you need to use 11 instead of 10, because the range [-5,5] (inclusive) contains 11 elements:
float x = ((int)arc4random_uniform(11) - 5) * delta;
arc4random returns a u_int32_t, an unsigned type. The modulus is also performed using unsigned arithmetic, which yields a number between 0 and 9, as expected (by the way, don't ever do this; use arc4random_uniform instead). You then subtract 5, which is interpreted as an unsigned value, yielding a possibly huge positive value due to underflow.
The solution is to explicitly type the 5 by storing it in a variable of signed type or with a suffix (like 5L).
Looks like arc4random % 10 becomes less than 5, and you are working with negative integer later.
What is the value of delta?
Look at my simple math script
double s = 3/2;
NSLog (#"%.2f",s);
I get 1, it should be 1.50
How can I fix it?
double s = 3/2 means divide the int 3 by the int 2, and then cast the result (which is the int 1) to a double (giving you 1.0).
You want this:
double s = 3.0/2.0;
try double s = 3/2.0
both 3 and 2 are integers, so despite receiver being double, you still get an int result and it is then converted to double
3 and 2 are integers. So 3/2 is 1. You should try instead
double s = 3.0/2.0;
NSLog (#"%1.2f",s);
It will give you the right answer.
I have a double that I need only the value of everything before the decimal point.
Currently I am using
NSString *level = [NSString stringWithFormat:#"%.1f",doubleLevel];
but when given a value of 9.96, this returns "10". So it is rounding. I need it to return only the "9". (note - when the value is 9.95, it correctly returns the "9" value.)
Any suggestions?
Thank You.
Simply assign the float/double value to a int value.
int intValue = doubleLevel;
Cast that baby as an int.
int castedDouble = doubleLevel;
Anything after the . in the double will be truncated.
9.1239809384 --> 9
123.90454980 --> 123
No rounding, simple truncation.
If you want to keep it as a float:
CGFloat f = 9.99;
f = floorf(f);
there are quite a variety of floor and round implementations.
they have been around since UN*X, and are actually part of those low-level libraries, be they BSD, Posix, or some other variety - you should make yourself familiar with them.
there are different versions for different "depths" of floating point variables.
NSString *level = [NSString stringWithFormat:#"%d",doubleLevel];
I am trying to convert an int to a string in objective-C.
I read the other questions on SO about converting ints to strings, and I tried this method in my code:
-(void)setCounter:(int)count
{
counterText.text = [NSString stringWithFormat:#"%d",count];
}
However, if I want to display a number like '01' the 0 is taken out of the conversion and only '1' is displayed. Is there a workaround?
There is no such number as 01. If you write
int count = 01;
it is compiled equivalently to
int count = 1;
In fact, be careful: 07 is equivalent to 7, but 011 is equivalent to 9!
What you can do is ask stringWithFormat: to give you the zero-padding:
[NSString stringWithFormat:#"%02d",count]
should give you "02" if count is 2. To deconstruct it:
% - interpolate the next value here
0 - pad it to the width by placing zeroes on the left side
2 - width is 2 characters
d - it will be an integer. Do it now.
If you want a different format to the one shown, use it:
counterText.text = [NSString stringWithFormat:#"%02d",count];
There are a huge range of possibilities with the format string.
if any number start from 0 then Its a octal representation (0 - 7). you can add zero explictly using below line.
counterText.text = [NSString stringWithFormat:#"0%d",count];
Check out..
NSNumber +numberWithInt
and then:
NSNumberFormatter -setMinimumIntegerDigits
and then get the string representation with:
NSString -stringFromNumber