The switch statement in C# is a control flow statement that allows you to select one of many code blocks to execute, based on the value of a variable or expression. It's a more readable alternative to using multiple if-else if statements when you need to compare a single variable against several possible values.

1. Syntax of switch Statement

switch (expression)
{
    case value1:
        // Code block to execute if expression equals value1
        break;

    case value2:
        // Code block to execute if expression equals value2
        break;

    // You can add more cases as needed
    default:
        // Code block to execute if none of the cases match
        break;
}

Key Parts:

• expression: The value or variable being evaluated (must be of a primitive type, enum, or string).
• case value1, case value2, ...: These define the specific values that expression is compared against. Each case is followed by a block of code to execute if the case matches.
• break: Terminates the switch statement to prevent fall-through to the next case.
• default: An optional block that executes if none of the specified case values match the expression. Think of it as the equivalent of the else in an if-else statement.

2. Example of a Simple switch Statement

int day = 3;

switch (day)
{
    case 1:
        Console.WriteLine("Monday");
        break;

    case 2:
        Console.WriteLine("Tuesday");
        break;

    case 3:
        Console.WriteLine("Wednesday");
        break;

    case 4:
        Console.WriteLine("Thursday");
        break;

    case 5:
        Console.WriteLine("Friday");
        break;

    default:
        Console.WriteLine("Weekend");
        break;
}

Explanation:

• In this example, day is evaluated.
• If day equals 1, it prints "Monday", and then the break statement terminates the switch.
• If day equals 2, it prints "Tuesday", and so on.
• If day doesn’t match any of the case values, the default block is executed, printing "Weekend".

3. Why Use switch Instead of if-else?

• Readability: When you need to check a single variable against multiple specific values, switch statements make your code more organized and easier to read compared to multiple if-else if conditions.
• Performance: In some cases, the switch statement can be more efficient than an if-else if chain, especially when dealing with many possible values.

4. Example with Strings in switch

You can also use strings in a switch statement:

string fruit = "Apple";

switch (fruit)
{
    case "Apple":
        Console.WriteLine("You chose Apple.");
        break;

    case "Banana":
        Console.WriteLine("You chose Banana.");
        break;

    case "Orange":
        Console.WriteLine("You chose Orange.");
        break;

    default:
        Console.WriteLine("Unknown fruit.");
        break;
}

Explanation:

• The value of fruit is compared with each case. If it matches "Apple", the code prints "You chose Apple." and then breaks.
• If the fruit doesn’t match any case, the default block runs, printing "Unknown fruit."

5. Fall-Through in switch Statement

In C#, switch statements do not allow implicit fall-through between cases, meaning each case must end with a break, return, or another terminating statement.

However, you can explicitly group cases if you want multiple cases to execute the same code:

int number = 2;

switch (number)
{
    case 1:
    case 2:
    case 3:
        Console.WriteLine("The number is between 1 and 3.");
        break;

    case 4:
    case 5:
        Console.WriteLine("The number is either 4 or 5.");
        break;

    default:
        Console.WriteLine("The number is outside the range.");
        break;
}

Explanation:

• In this example, case 1, case 2, and case 3 are grouped to execute the same block of code if the number is between 1 and 3.

6. Example with Enums

switch statements work well with enums. Enums represent a set of named constants and can make your code more readable:

enum Day
{
    Monday,
    Tuesday,
    Wednesday,
    Thursday,
    Friday,
    Saturday,
    Sunday
}

Day today = Day.Tuesday;

switch (today)
{
    case Day.Monday:
        Console.WriteLine("Today is Monday.");
        break;

    case Day.Tuesday:
        Console.WriteLine("Today is Tuesday.");
        break;

    case Day.Wednesday:
        Console.WriteLine("Today is Wednesday.");
        break;

    default:
        Console.WriteLine("It's a weekend!");
        break;
}

Explanation:

• Here, today is an enum value of type Day.
• The switch statement checks the day and prints the corresponding message.
• This is useful for making your code more readable and less prone to errors.

7. Using switch with Ranges (C# 8.0 and above)

Starting with C# 8.0, you can use pattern matching in switch statements to handle more complex conditions, including ranges:

int grade = 85;

switch (grade)
{
    case int g when g >= 90:
        Console.WriteLine("A");
        break;

    case int g when g >= 80:
        Console.WriteLine("B");
        break;

    case int g when g >= 70:
        Console.WriteLine("C");
        break;

    default:
        Console.WriteLine("F");
        break;
}

Explanation:

• Here, we use a switch expression to classify the grade.
• The keyword when is used to apply a condition (in this case, a range of values).
• If grade is 90 or above, it prints "A". If it’s between 80 and 89, it prints "B", and so on.

8. Example with Return Statement in switch

In some cases, you may want to return a value directly from a switch statement without using break.

int number = 3;

string result = number switch
{
    1 => "One",
    2 => "Two",
    3 => "Three",
    _ => "Unknown number"
};

Console.WriteLine(result);

Explanation:

• In C# 8.0 and later, you can use the expression form of switch which allows you to directly return a value from the switch statement without using break.
• Here, if number equals 1, 2, or 3, the corresponding string is returned. The underscore (_) represents the default case (if no match is found).

9. Summary of switch Statement

• The switch statement provides a cleaner way to compare a single expression against multiple values.
• case blocks handle specific values, and the default case provides a fallback if no match is found.
• Break statements are used to prevent fall-through, although cases can be grouped when needed.
• The switch statement is useful for handling both primitive types (like int, char, etc.) and complex types such as string and enum.
• Starting from C# 8.0, pattern matching and range checks are supported in switch expressions, allowing more advanced scenarios.

This flexibility makes the switch statement an essential part of decision-making logic in C# programs.