The switch statement in C++ is used to simplify the code when you have multiple possible values for a single expression. It evaluates an expression and matches it against multiple case values, executing the code associated with the matching case. This structure is often used as an alternative to a series of if-else if statements when checking for equality.

Syntax of switch Statement

switch (expression) {
    case value1:
        // Code to execute if expression == value1
        break;
    case value2:
        // Code to execute if expression == value2
        break;
    // More cases...
    default:
        // Code to execute if no case matches
}

• expression: This is evaluated once and compared with each case value.
• case value:: The value to match against the expression.
• break: Used to exit the switch block. Without break, the code will continue executing the subsequent cases, known as "fall-through."
• default:: The default block executes if none of the case values match. It is similar to the else statement in an if-else structure.

Example: Days of the Week

Here is an example using switch to determine the day of the week:

#include <iostream>

int main() {
    int day;
    std::cout << "Enter a day number (1-7): ";
    std::cin >> day;

    switch (day) {
        case 1:
            std::cout << "Monday" << std::endl;
            break;
        case 2:
            std::cout << "Tuesday" << std::endl;
            break;
        case 3:
            std::cout << "Wednesday" << std::endl;
            break;
        case 4:
            std::cout << "Thursday" << std::endl;
            break;
        case 5:
            std::cout << "Friday" << std::endl;
            break;
        case 6:
            std::cout << "Saturday" << std::endl;
            break;
        case 7:
            std::cout << "Sunday" << std::endl;
            break;
        default:
            std::cout << "Invalid day number" << std::endl;
    }

    return 0;
}

Explanation

• switch (day): The value of day is evaluated, and the switch block attempts to match it with one of the case values.
• Each case represents a possible value for day. For instance, if the user enters 3, the program outputs "Wednesday."
• The break statement is used to terminate a case block. Without break, the program will "fall through" and execute the code in the following cases, which is often undesirable.
• default is used to handle cases where none of the case values match the given day. For instance, if the user enters a value outside of 1-7, the output will be "Invalid day number."

Example with Fall-Through

If you omit the break statement, the code continues to execute the following cases even if a match was found. This is called "fall-through" and can sometimes be useful.

#include <iostream>

int main() {
    int num = 2;

    switch (num) {
        case 1:
            std::cout << "Number is One" << std::endl;
        case 2:
            std::cout << "Number is Two" << std::endl;
        case 3:
            std::cout << "Number is Three" << std::endl;
        default:
            std::cout << "End of switch" << std::endl;
    }

    return 0;
}

Output:

Number is Two
Number is Three
End of switch

In this example, since there are no break statements, the code falls through from case 2 to case 3 and then to default.

Key Points

1. Single Expression: The switch statement works best for a single expression that can be compared against multiple constant values.
2. break Statement: Always use break unless you intentionally want to fall through to the next case.
3. default: The default block is optional, but it is recommended to handle unexpected values.

Use Cases

• Simplifies code when you have multiple possible discrete values for a single variable.
• Often used for menu selection, input handling, and managing different modes or states in a program.

The switch statement provides an easy-to-read alternative to complex if-else if chains when dealing with many specific values for a single variable.