Question

Given that Decimal.MaxValue = 79228162514264337593543950335m

Why does the next line give me 7922816251426433759354395034M in the Local window instead of 7922816251426433759354395033.5m as expected?

Decimal target = Decimal.MaxValue / 10m;

Answer 1

I suspect this is a compiler error, actually.

Here’s a short but complete program to show why I think that:

using System;  class Test {     static void Main()     {         decimal constant = decimal.MaxValue / 10m;         decimal calculated = decimal.MaxValue;         calculated /= 10m;          Console.WriteLine (constant);         Console.WriteLine (calculated);             } } 

Output:

7922816251426433759354395034 7922816251426433759354395033.5 

I’ll dig into the spec to see what guarantees are given.

EDIT: In the spec, section 7.18 claims:

The compile-time evaluation of constant expressions uses the same rules as run-time evaluation of non-constant expressions, except that where run-time evaluation would have thrown an exception, compile-time evaluation causes a compile-time error to occur.

That’s clearly not the case here. Hmm.

EDIT: I’ve submitted a bug to Microsoft Connect. We’ll see what happens to it.