Ternary Operator

At the end of this lesson, you should be able to answer the following:

• What is the ternary operator?

• Where can I use the ternary operator?

• How do I use the ternary operator in an expression?

In Lesson 7, we learned about the if-else statement that lets us represent a branching path in our programs. In this lesson, we will learn another way to depict a conditional expression.

The ternary operator ?: is useful to make quick if-else conditions that evaluates to a result.

var isFemale = true;
var evolvedForm = isFemale ? "Nidorina" : "Nidorino";

Line 2 is using a ternary operator expression, in conjunction with a variable declaration. We have declared a variable named evolvedForm. Can you guess what type this variable will be?

evolvedForm is a string variable. The inferred value comes from the result of the ternary operator expression. Let's break it down:

• First is isFemale, followed by a ?. The part that comes before the ? is the condition. isFemale is a boolean variable declared in Line 1, with the value of true.

• Next is a string value, Nidorina, followed by a :. The part that comes before the : is the result of the whole expression when the condition is true.

• Finally we have the string value Nidorino after the :. The part that comes after the : is the else clause or alternate path - the result of the expression when the condition is false.

In short, the syntax of the ternary operator expression is:

<condition> ? <result-if-true> : <result-if-false>

Run the code and add a Console.WriteLine(evolvedForm); statement to display the result. Can you guess what the value of evolvedForm will be? How about if isFemale is set to false?

Here's what our code will look like as a regular if-else statement.

var isFemale = true;

string evolvedForm;
if (isFemale) 
{
    evolvedForm = "Nidorina";
}
else
{
    evolvedForm = "Nidorino";
}

As we can see, using the ternary operator makes for more concise code!

Just like a regular if-else statement, the condition part of the ternary operator (the part before the ?) can have more complex conditional expressions, like age > 20.

We can even chain ternary expressions. Use this sparingly, however - it can affect the readability of our code. Below, the result of the first ternary expression has been indented so it's easier to read the code.

var isFemale = false;
var finalEvolution = true;

var evolvedForm = isFemale ? 
        finalEvolution ? "Nidoqueen" : "Nidorina" :
        finalEvolution ? "Nidoking" : "Nidorino";
        
Console.WriteLine(evolvedForm);

Challenge

Using the first example in this lesson as a guide, change the if-else statement in the piece of code below to use a ternary expression.

if (age < 16)
{
    Console.WriteLine("You're not allowed to drive yet.");
}
else
{
    Console.WriteLine("You're allowed to drive.");
}