[FIXED] Why .0 is dropped in division but not in +, - and *?

Issue

So, as per C# rules, in the division (int & int division) the output is an int. While in (FP & int division), it is a FP.

but following generate different outputs.

int a = 45; //integer
decimal b = 5.0m; //floating point
Console.WriteLine(a/b); // "9"

Output is: 9 //output looks like an integer??? why?

Note that +, -, and * produce expected result:

  Console.WriteLine(a * b); // "225.0"

Dividing by non whole number produce expected result:

int a = 45; //integer
decimal b = 5.5m; //floating point
Console.WriteLine(a/b); // "8.181818181818181818"

Output is: 8.181818181818181818 - / output is a FP which is okay.

Can anyone explain this?

The results are more consistent for float / double - no zeros in output for all operations (which makes sense as those types don't store infomration on number of digits after decimal point)

Solution

The C# standard goes into details here, in section 12.9.3.

The scale of the result, before any rounding, is the closest scale to the preferred scale that will preserve a result equal to the exact result. The preferred scale is the scale of x less the scale of y.

So, to apply that, we've got x with a value of 45m (after an implicit conversion to decimal) which has a scale of 0, and 5.0m which has a scale of 1.

Therefore the preferred scale is -1 - which would be invalid. (The scale is always non-negative.) The closest scale that can preserve the exact result is 0, so that's the actual scale - the result is equivalent to 9m rather than 9.0m.

Answered By - Jon Skeet

Answer Checked By - Clifford M. (PHPFixing Volunteer)