What is the difference between 0d and (double)0?

Question

Example 1:

if ((Value ?? 0d) <= 0d)
{
    //some code
}

Example 2:

if ((Value ?? (double)0) <= (double)0)
{
    //some code
}

What is the difference between these two? and which one is better to use?

Answer 1

Both code snippets are equivalent, as the type-cast will be performed by the compiler at compile-time, and the result treated as a constant. Note that this is standard behaviour, not just a compiler optimization; otherwise, you would not be able to use casts for constants:

    const double d1 = (double)0;          // allowed
    const double d2 = Math.Pow(2, 4);     // error: "The expression being assigned to 'd2' must be constant"

Specifying the proper literal suffix is nonetheless preferred as it keeps your code concise. Another popular convention for specifying doubles is to append .0:

if ((Value ?? 0.0) <= 0.0)

Answer 2

The first one is better.

Second one makes the cast happen at runtime. First one declares constant as double right away.