What is and how to use the conditional SWITCH in C#

The switch conditional is a control structure in C# that provides a way to execute different blocks of code depending on the value of an expression.

Sometimes it is used as a cleaner and more readable alternative to a series of nested if-else statements. Although, many people think (myself included) that instead of improving readability, it usually worsens it.

The switch conditional allows evaluating the value of an expression and executing specific code blocks based on different possible values of that expression.

The basic syntax of a switch conditional in C# is as follows:

switch (expression)
{
    case value1:
        // Code to execute if expression is equal to value1
        break;
    case value2:
        // Code to execute if expression is equal to value2
        break;
    ...
    default:
        // Code to execute if expression does not match any case
        break;
}

• expression: It is the expression whose value is evaluated in each case.
• case: Represents a specific value that is compared with the expression.
• Default: Optionally, a default block can be included that will be executed if none of the cases match the value of the expression.

The default block will be executed if none of the previous cases match the value of the expression. It is optional, but it is most normal to have it.

Let’s see it with a simple example where a switch conditional is used to print a number on the screen.

int number = 2;

switch (number)
{
    case 1:
        Console.WriteLine("One");
        break;
    case 2:
        Console.WriteLine("Two");
        break;
    case 3:
        Console.WriteLine("Three");
        break;
    default:
        Console.WriteLine("Invalid number");
        break;
}

In this case, depending on the value of number

• 1, 2, and 3 will print the corresponding number on the screen.
• Any other number will show “Invalid number”.

Fall-Through between cases

Fall-Through is the possibility of “falling” from one case to another, and executing several code statements. Unlike other languages (such as C++), “fall-through” is intentionally limited.

In C# all blocks must

• Either be empty
• Or have a break statement.

That is, it is not possible to do this by omitting the break in a case,

case 1:
	Console.WriteLine("One");
	// I can't not put `break`
case 2:
	Console.Writeline("Two");
// more cases

It would be possible if the case are completely empty. Like this

switch (number)
{
    case 1:
    case 2:
    case 3:      
        Console.WriteLine("Less than 3");
        break;
    default:
        Console.WriteLine("Greater than 3");
        break;
}

Although, it is most likely a bad idea to do so 😉.

Practical examples

Determine the name of a number

In this example, we use the switch structure to determine the name of a number according to its value.

int number = 2;

// We use switch to determine the name of the number according to its value
switch (number)
{
    case 1:
        Console.WriteLine("One");
    case 2:
        Console.WriteLine("Two");
        break;
    case 3:
        Console.WriteLine("Three");
        break;
    default:
        Console.WriteLine("Invalid number");
        break;
}

Determine the mathematical operation according to the operator

This code shows how to use a switch to determine the mathematical operation according to the provided operator.

char operator = '+';

// We use switch to determine the mathematical operation according to the operator
switch (operator)
{
    case '+':
        Console.WriteLine("Sum");
        break;
    case '-':
        Console.WriteLine("Subtraction");
        break;
    case '*':
        Console.WriteLine("Multiplication");
        break;
    case '/':
        Console.WriteLine("Division");
        break;
    default:
        Console.WriteLine("Invalid operator");
        break;
}

Determine the name of a day of the week

This example shows how to determine the name of a day of the week using a switch structure.

int day = 3;

// We use switch to determine the name of the day according to its value
switch (day)
{
    case 1:
        Console.WriteLine("Monday");
        break;
    case 2:
        Console.WriteLine("Tuesday");
        break;
    case 3:
        Console.WriteLine("Wednesday");
        break;
    // Add cases for the remaining days...
    default:
        Console.WriteLine("Invalid day");
        break;
}

Determine the name of a month (with enumeration)

Here a switch is used to determine the name of a month according to its value in an enumeration.

// We define an enumeration for the months of the year
enum Months { January = 1, February, March, April, May, June, July, August, September, October, November, December }

// We declare a variable of the enumeration to represent the month
Months month = Months.May;

// We use switch to determine the name of the month according to its value in the enumeration
switch (month)
{
    case Months.January:
        Console.WriteLine("January");
        break;
    case Months.February:
        Console.WriteLine("February");
        break;
    // Add cases for the remaining months...
    default:
        Console.WriteLine("Invalid month");
        break;
}