[stevenwoo]

There's the theory that any hardcoded constant directly in code is bad idea. It may be used more than once, or used only once now, but in the future used more than once, or in the future the value may be changed and if it's used more than once, this is a source of issues.

[yongjik]

I get that using hard-coded constant is a bad idea, but using ASCII_A instead of 'A' is about as sensible as using SIXTY_FOUR instead of 64.

If A signifies something else, use that name; otherwise just use plain 'A': it already gives us as much information as needed, and has one less place where the programmer can screw up.

[robotresearcher]

I get that in general. It depends if the code is meant to inspect the character x on this machine right now, or really the ASCII character x.

As an aside, if someone changes the constant value of ‘A’ now, the world will be broken for a while. (But my code would recompile correctly unchanged with the new standard header.)