Why c# decimals can't be initialized without the M suffix?

Question

public class MyClass
{
    public const Decimal CONSTANT = 0.50; // ERROR CS0664   
}

produces this error:

error CS0664: Lit

Answer 1

From http://msdn.microsoft.com/en-us/library/364x0z75.aspx : There is no implicit conversion between floating-point types and the decimal type; therefore, a cast must be used to convert between these two types.

They do this because double has such a huge range ±5.0 × 10−³²⁴ to ±1.7 × 10³⁰⁸ whereas int is only -2,147,483,648 to 2,147,483,647. A decimal's range is (-7.9 x 10²⁸ to 7.9 x 10²⁸) / (10^{0 to 28}) so it can hold an int but not a double.