I suppose you could create a dictionary of opcode -> function pointers. In C# that'd be like

    var ops = new Dictionary<Opcode, Action<opcodeArgs>> ()
    { 
        {0, nop },
        {1, add },
        ...
    }

or even better, maybe I'd get a list of the opcodes with their names, name all the functions after those names exactly, then use reflection to automatically create this dictionary.

Then in the main loop,

    ops[opcode].Invoke(args);

I don't know if something like that would be any use in C, though.