C++ switch Statement

switch chooses one path from many, by the value of an integer, a char or an enum (not a string or a double).

#include <iostream>

int main() {
    int day = 3;
    switch (day) {
        case 1:
            std::cout << "Monday\n";
            break;
        case 2:
            std::cout << "Tuesday\n";
            break;
        case 3:
            std::cout << "Wednesday\n";
            break;
        default:
            std::cout << "Another day\n";
    }
}

Fall through

Without break the code goes on to the next case. It is useful to group cases, but it is also a common bug. Use [[fallthrough]]; when you really want it.

#include <iostream>

int main() {
    char grade = 'B';
    switch (grade) {
        case 'A':
        case 'B':
            std::cout << "Good ";
            [[fallthrough]];
        case 'C':
            std::cout << "Pass\n";
            break;
        default:
            std::cout << "Fail\n";
    }
}

Switch with an enum class

#include <iostream>

enum class Level { Low, Medium, High };

int main() {
    Level level = Level::High;
    switch (level) {
        case Level::Low:    std::cout << "All fine\n"; break;
        case Level::Medium: std::cout << "Be careful\n"; break;
        case Level::High:   std::cout << "Danger\n"; break;
    }
}

If you forget one value of the enum (and no default), the compiler warns you with -Wall.

Variables inside a case

#include <iostream>

int main() {
    int n = 1;
    switch (n) {
        case 1:
            int x = 10;             // jumping over this initialization from another case is an error
            std::cout << x << '\n';
            break;
        case 2:
            std::cout << "two\n";
            break;
    }
}

Put the case code in braces { } when you declare variables in it.

Switch with an initializer (C++17)

#include <iostream>

int main() {
    switch (int code = 404; code) {
        case 200: std::cout << "OK\n"; break;
        case 404: std::cout << "Not found\n"; break;
        default:  std::cout << "Other\n";
    }
}

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