C++ Switch Statement: Jump Tables, Rules & Modern [[fallthrough]]

The switch statement is a multi-way branch selection control structure. It tests an expression against a list of constant integral values (case labels). Compilers often optimize switch into an $O(1)$ Jump Table, executing substantially faster than long if-else ladders.

Switch Syntax with C++17 [[fallthrough]]

#include <iostream>

enum class Severity { Low, Medium, High, Critical };

void processAlert(Severity level) {
    switch (level) {
        case Severity::Low:
            std::cout << "[INFO]: Minor event logged.\n";
            break;
        case Severity::Medium:
            std::cout << "[WARN]: Check system diagnostics.\n";
            break;
        case Severity::Critical:
            std::cout << "[CRITICAL]: Send emergency notification!\n";
            [[fallthrough]]; // C++17 attribute: Intentionally cascades to High
        case Severity::High:
            std::cout << "[HIGH]: Alert duty engineer immediately.\n";
            break;
        default:
            std::cout << "[UNKNOWN]: Invalid severity code.\n";
            break;
    }
}

int main() {
    processAlert(Severity::Critical);
    return 0;
}