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Trying to optimize may lead to errors and high-maintenance/change-resistant code. If there’s no need to optimize, let the code be.

Only optimize performance-critical parts of a program. If your program spends 4% of its processing time doing computation A, and 40% of its time doing computation B, a 50% improvement on A is only as impactful as a 5% improvement on B.

Complicated and/or low-level code is not necessarily faster than simple code. Optimizers sometimes do marvels with simple and/or high-level code.

Unscoped (or Plain or C-Style) Enumerations

Plain (or C-style) enums are entered in the same scope as the name of their enum, and implicitly convert to their integer value, e.g.

enum Color { red, green, blue };
int col = green;
Color c2 = 1; // error: invalid conversion from 'int' to 'Color' [-fpermissive]

enum CardColor { red, black }; // Error: "red" conflicts with a previous declaration

The name can be omitted if it’s not going to be used, e.g.

enum { red, green, blue };
int col = red;

.

Unnamed enums are common in code written before alternative ways of specifying integer constants, e.g.