A "switch" statement, also known as a "switch case" statement, is a control flow structure in many programming languages that allows you to select and execute one of several code blocks (or "cases") based on the value of an expression. It's often used when you have a single variable or expression and you want to perform different actions depending on its value.


Here's a basic explanation of how a switch case statement works:


1. **Syntax**: The basic syntax of a switch case statement looks like this in many programming languages, including C, C++, Java, and others:


``` 

switch (expression) {

    case value1:

        // Code to execute if expression matches value1

        break;

    case value2:

        // Code to execute if expression matches value2

        break;

    // ... more cases ...

    default:

        // Code to execute if expression doesn't match any case

}

```


- `expression`: This is the value or expression that you want to evaluate.

- `case value1:`: This is one of the possible values that `expression` can take. If `expression` is equal to `value1`, the code block following this case is executed.

- `break`: The `break` statement is used to exit the switch statement after a case has been executed. Without `break`, the code would continue executing for all subsequent cases, including those that don't match the expression.


2. **How it works**: The expression is evaluated, and the program flow enters the switch statement. The program then looks for the first case label that matches the value of the expression. If a match is found, the code block associated with that case is executed. If there is no match, the code block under the `default` label (if it exists) is executed.


3. **Optional "default" case**: The `default` case is optional, and it serves as a catch-all case that executes if none of the other case labels match the expression. It's often used for error handling or to specify a default behavior when no specific match is found.


Here's a simple example in C++ to illustrate how a switch case statement works:


```cpp

#include <iostream>


int main() {

    int choice = 2;

    

    switch (choice) {

        case 1:

            std::cout << "You chose option 1" << std::endl;

            break;

        case 2:

            std::cout << "You chose option 2" << std::endl;

            break;

        case 3:

            std::cout << "You chose option 3" << std::endl;

            break;

        default:

            std::cout << "Invalid choice" << std::endl;

    }


    return 0;

}

```


In this example, if the `choice` variable is 2, it will print "You chose option 2" to the console because it matches the case label for 2. If `choice` had a different value, it would execute the `default` case.


Switch case statements are a convenient way to write code that makes decisions based on the value of a single variable or expression, and they're often used in menu systems, state machines, and other situations where you need to choose between multiple actions.