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.
