C＃中的运算符优先级

Question

Is

(int)(int1 / (float)var2.Count() * 100)

equivalent to

(int)((int1 / (float)var2.Count()) * 100)

...and will it use floating point or integer division?

Edit... if the answer is yes to the above, what is the advantage of performing a floating point division here?

Answer 1

/ and * have the same operator precedence, under §7.2.1 so the two results should be the same (using float rules).

I, however, can't be bothered to learn precedence tables; I just use brackets. Then it works in any language without needing to remember it.

Another important question is the rounding in the final (int) cast: do you expect that to be "up", "down" or "bankers"?

Answer 2

Precedence rules are really annoying to remember, so I too prefer to use brackets to disambiguate. I try to follow the advice to "write code for people first, computers second". But, there's an interesting mnemonic (that I learned from Bruce Eckel's books) to remember (some of) the rules: " Ulcer Addicts Really Like CA lot ":

Ulcer   - Unary (+, -, ++, --, !)
Addicts - Arithmetic (and shift) (+, -, *, /, %, <<, >>)
Really  - Relational (<, >, ==, <=, >=, !=)
Like    - Logical (and bitwise) (&&, ||, &, |, ^)
C       - Conditional ( ? : ) <- this is the conditional ternary operator
A lot   - Assignment ( =, *=, +=, ...)

It's not perfect, bitwise operators are squeezed in and we have to know that multiplication operators (*, /, %) take precedence over addition ones (+, -).

Answer 3

They are equivalent and it will use floating point division. Even if the multiplication happened first, floating point division would be used since the int is divided by the result of float*int which is float.

Edit:

If the answer is yes to the above, what is the advantage of performing a floating point division here?

Is it an advantage? The first thing that you should be considering is whether or not it's correct since the result will be different. Judging by the code it seems you are trying to calculate some percentage. When using integer divison, if "int1" is always smaller than var2.Count() the result will always be 0 which might not be what you want.

Answer 4

I would say Yes, division and multiplication should go left-to-right. And thus it is a float division.

PS: replace float with double wherever you can.

Answer 5

请参阅C＃语言规范： 运算符优先级和关联性 。

Answer 6

It's the same. Both will use float division.

Answer 7

yes both are equivalent.

Both will use floating point division.

Answer 8

整数除法只会给出答案的整个部分，即3/2将为1而浮点除法将给出1.5