问题
I'm trying to calculate some numbers in an iPhone application.
int i = 12;
int o = (60 / (i * 50)) * 1000;
I would expect o to be 100 (that's milliseconds) in this example but it equals 0 as displayed by NSLog(@"%d", o).
This also equals 0.
int o = 60 / (i * 50) * 1000;
This equals 250,000, which is straight left-to-right math.
int o = 60 / i * 50 * 1000;
What's flying over my head here?
Thanks,
Nick
回答1:
In Objective-C / performs integer division on integer arguments, so 4/5 is truncated to 0, 3/2 is truncated to 1, and so on. You probably want to cast some of your numbers to floating-point forms before performing division.
You're also running in to issues with precedence. In the expression
60 / (i * 50) * 1000
the term inside the parentheses is calculated first, so 60 is divided by 600 which produces the result 0. In
60 / i * 50 * 1000
the first operation is to divide 60 by 12 which gives the result 5 and then the multiplications are carried out.
回答2:
An integer divided by an integer is an integer.
so 60/600 is not 0.1, it is 0.
Cast (or declare) some stuff as float instead.
回答3:
Replace:
int o = (60 / (i * 50)) * 1000;
with:
int o = 1200/i;
回答4:
It's doing integer math. 60 / (12 * 50) is 0.1, truncates to 0.
Should work if you force floating point and then cast back to an integer.
int o = (int)(60.0 / ((double) i / 50.0) * 1000.0;
Probably not really necessary to make everything a double.
回答5:
By order of precedence, the operation:
60 / (12 * 50)
is performed before multiplying by 1000.
This value is less than 1 and is cast to an int, which truncates it to 0. And 0 times anything is 0.
Use a float or first multiply by 1000 to ensure you're not ending up with propagating a 0 in your calculations.
回答6:
All the operations in your expression are performed in integer arithmetic, meaning that the fractional part of each intermediate result is truncated. This means that if you divide a smaller integer by a larger integer you will always get 0.
To get the result you want you must either make sure the operations are performed in a particular order, or you must use floats. For example the result of
int o = (60.0 / (i * 50.0)) * 1000.0;
should be o = 100.
回答7:
I think you need to use float here instead of int. It will work the way you want! Will give you answer in decimals as well.
来源：https://stackoverflow.com/questions/4197841/objective-c-integer-arithmetic