25. Selection expressions

Now that we have an understanding of how to control the flow of our programs using selection statements, let’s look at how we can achieve similar functionality with a more compact syntax using selection expressions. Selection expressions are an elegant way to select between two or more expressions based on a condition.

As you may recall, the key difference between statements and expressions in C# lies in how they’re used and what they produce. A statement performs an action and doesn’t return a value. It’s like a command that you give to the computer. An expression, on the other hand, evaluates to a value and can be used as a part of larger expressions or statements. In other words, an expression is a piece of code that produces a value.

In the context of this chapter, the ternary conditional operator and switch expressions are selection expressions. This means they evaluate a condition and produce a value based on that condition. This contrasts with the selection statements we discussed in the previous chapter, which perform actions based on conditions but do not produce values.

Ternary Conditional Operator

One of the most common selection expressions in C# is the ternary conditional operator, which is written as ?. The ternary operator takes three operands: a condition to check, a result for true, and a result for false.

Here’s how you use it:

int a = 10;
int b = 20;

string result = (a > b) ? "A" : "B";

Console.WriteLine(result);

The below script needs to be able to find the current output cell; this is an easy method to get it.

B

In this code, the condition expression a > b is checked. If it evaluates to true, "A" is assigned to the variable result, but if it evaluates to false then "B" is assigned.

Switch Expressions

Switch expressions provide a more concise syntax than switch statements for some common scenarios.

Here’s an example of a switch expression:

var day = DayOfWeek.Mon;

string dayType = day switch
{
    DayOfWeek.Sat => "Weekend",
    DayOfWeek.Sun => "Weekend",
    _ => "Weekday"
};

Console.WriteLine(dayType);

enum DayOfWeek { Mon, Tue, Wed, Thu, Fri, Sat, Sun };

Weekday

In this code, the variable day is being switched upon. If day is Sat or Sun, the string "Weekend" is assigned to the variable dayType. For any other day, "Weekday" is assigned. The _ is a discard pattern that matches anything, similar to the default case in a switch statement. We’ll learn more about pattern matching in a later chapter.

Both ternary conditional operators and switch expressions allow us to express selection in a concise and elegant way, especially in scenarios where the code primarily assigns values based on conditions. They are powerful tools in any C# programmer’s toolbox!