What is the difference between... uh, I need to show you

[silver_star]

Basically,

and

[programmer_user]

The first one can take inputs, the second one can't.
The first one can be any expression, the second one can't.

[pumpkinhead]

the difference between a command ring and a C-slot is that the C-slot is better suited for longer block stacks, and that you can't write formal parameters in the C-slot.

[ego-lay_atman-bay]

@programmer_user

The first one can be any expression, the second one can't.

the second one can. You can drop a reporter in the c-shape (in custom blocks, not primitives).

[bh]

There's a pedagogic difference: The command ring makes explicit the fact that what's inside it is a reified script. (That's true for a C-shaped slot, too, but they don't rub your nose in it.) But the C-shaped slot has a meaning that's instantly obvious to new users (one of the brilliant pieces of the Scratch visual design).

Since primitives with C-slots don't let you drop a variable onto the slot (a misfeature imho but never mind...), we have to use a command ring in the RUN block and friends (e.g. TELL) because it's more common to want to use a variable as the argument than to have an explicit script. (Well, definitely more common for RUN. For TELL I don't know which is more common, but at least using a variable is pretty common.)