Why I cannot the get percentage by using Int

问题

Please forgive my programming knowledge. I know this is a simple thing, but I do not understand why result is always 0. Why decimal will be fine?

int a = 100;
int b = 200;
decimal c = (a / b) * 100;

Many thanks.

回答1:

Integer division always truncates the remainder. This is done at the time that the number is divided, not when it's assigned to the variable (as I'm guessing you assumed).

decimal c = ((decimal)a / b) * 100;

回答2:

The value a/b will return 0 always since they are integers. So when the values within the Brackets are evaluated you are technically doing this

decimal c = (0) * 100

Better do,

decimal c = ((decimal)a/(decimal)b) * 100

回答3:

100 / 200 is 1/2 or 0.5. Since you are using ints, it rounds down to 0 (zero). And 0 * 100 is still 0. The part inside the parentheses is always evaluated first: if you want to get this working, use:

decimal c = (a * 100) / b;

Edit: if you want a more precise value rather than an "integer percentage" (ie. 33.333% instead of 33%), you should use Bragaadeesh's answer.

回答4:

Integer math is being performed, and the result is then being stored as a decimal. 100 / 200 in integer math is 0. To get your percentage, cast at least one value to decimal before doing the calculation.

decimal c = (a / (decimal)b) * 100;

回答5:

In strongly typed languages, the result of math operations is usually the same type as the larger type.

C# has a list of implicit numeric conversions it will do.

Generalizing this list: Integral types can be converted to floating point types, but not vice versa. Integral types can also be implicitly converted to decimal, but floating point types cannot.

Note: This also means that casting one of the ints to another type will result in the entire answer being that type. ex: (decimal) a / b * 100.0 = 50.0

tl;dr:

In C#:

int / int = int
int + decimal = decimal
decimal + int = decimal
int / int * decimal = (int / int = int) * decimal = decimal
int - float = float
int * double = double
float / decimal = an error
int - uint = an error (either that or ulong)

回答6:

The math being done is still integer math.

(a/b) (100/200 or 1/2) is done on two integers, so the result is zero. Zero * 100 is ... well, still zero.

The problem you are experiencing is with the order of operations (a and b are integers, so integer math is performed).

I suggest this:

decimal c=((decimal)a)/((decimal)b)*100;

This will force the math performed to the decimal values you seek.

回答7:

int can only be whole numbers, so 100/200 is going to be 0. 0*100 is still 0. Change the type to a decimal, and it will work

回答8:

Make it decimal c = (a * 100) / b;

回答9:

While using integers, this '/' stands for DIV and this '%' for MOD. DIV is the quotient of the division, MOD is the rest. So, 100/200 = 0 and 100%200 = 100.

So, you need to change a and b types to decimal, in your case.

来源：https://stackoverflow.com/questions/2602025/why-i-cannot-the-get-percentage-by-using-int

标签

integer-division