Prefer a `switch`-statement to an `if`-statement when there is a choice

Reason

• Readability.
• Efficiency: A switch compares against constants and is usually better optimized than a series of tests in an if-then-else chain.
• A switch enables some heuristic consistency checking. For example, have all values of an enum been covered? If not, is there a default?

Example

void use(int n)
{
    switch (n) {   // good
    case 0:
        // ...
        break;
    case 7:
        // ...
        break;
    default:
        // ...
        break;
    }
}

rather than:

void use2(int n)
{
    if (n == 0)   // bad: if-then-else chain comparing against a set of constants
        // ...
    else if (n == 7)
        // ...
}

Enforcement

Flag if-then-else chains that check against constants (only).