减去C＃中的百分比

Question

I'm trying to subtract percentage in C# using:

n = n - (n * 0.25);

but I'm getting an error:

"Cannot implicitly 'double' to 'int'. An explicit conversions exists (are you missing a cast?)"

Answer 1

Your value n is an int .

When you multiply by 0.25 ( which is a double ), the resulting value is a double that you try to assign to a int .

To solve it, you have to specify that you are aware that you will lose precision using "explicit conversion".

n = n - (int)(n * 0.25);

Doing (Type)value is called "to cast value to Type ". This is exactly what the error message suggest you to do.

Or, if you don't want to keep the precision, declare n not as an int but as a double . In this case, you will not have to cast n * 0.25 to int .

Answer 2

If you don't want to switch back and forwards between int and double types you could just use:

n = (n * 75) / 100

if your answer ever has decimals they'll be lost though

Answer 3

Your variable n must be an integer, but the result of your calculation is a double, since it involves multiplication by a double ( 0.25 ).

You can cast the result back to an int like this:

n = (int)(n - (n * 0.25));

Answer 4

I'm assuming that n is an integer type then, say int , as you don't give a clue to that. In which case the easiest solution is to do:

n = Convert.ToInt32(n - (n * 0.25));

Or you can cast:

n = (int)(n - (n * 0.25));

Answer 5

Check the type of variable 'n'.

Either 'n' should be of double type.

Or

Use explicit cast to convert to int.

int n = (int)(n - (n * 0.25));

Answer 6

Your n variable is an int . When you try to multiple with 0.25 , 0.25 is double , so result will be double . You should cast it manually because there is no Implicit Numeric Conversion for double to int . You have to use Explicit Numeric Conversion for them.

From --> To

double --> sbyte , byte, short, ushort, int, uint, long, ulong, char, float, or decimal

You should convert your right expression to int .

int n = 100;
n = (int) (n - (n * 0.25));
Console.WriteLine(n);

Here is a DEMO .

And remember;

• Explicit numeric conversion may cause loss of precision.
• When you convert from a double value to an integral type, the value is truncated. If the resulting integral value is outside the range of the destination value, the result depends on the overflow checking context.

Answer 7

你必须将结果转换为int

n=(int)(n-(n*0.25));

Answer 8

try:

n = n - (int)((double)n * 0.25);

note: by doing this you wont have numbers behind the point in the n result.

Answer 9

I guess this could be an issue with the type of n being int it least needs to be double

hence when you have n = n - (n * 0.25) the result is a double

if you want to cast it as int then beware of rounding since it would not always be ending in .00

Also i think this would be better n = n * 0.75

Answer 10

The best way would be to do

 n = n - n/4;

If you want a percentage to be a whole number between 0 and 100, otherwise you should declare n to be a double by replacing int n with double n . No costly conversion will occur in the proposed assignment. Note that n/4 is an integer because both operands ( n and 4 ) are integers, causing no promotions, thus using integer division.

Explanation

This is type promotion, n is multiplied by a double , which promotes n*0.25 automatically to a double . A primitive can only be promoted into a higher rank, not demoted to a lower rank. A primitive x is of a higher rank then another primitive y if it can hold all values of y without causing loss of precision. A double can hold all values of an integer, but an integer can, for example, not hold 0.1 . So you are trying to promote and demote. See MSDN library for more information.

Note: Casting from a double to an int causes the value to be truncated, that is all decimals after the 'dot' will be erased, so -2.5 becomes -2 and 1.5 becomes 1 . Integer division, as used above also rounds to zero, making this assignment equal with your assignment. But avoiding any costly conversions.