The ternary operator

C# course · Beginner · Lesson 40/116

Learn to write a conditional expression in one line with ? :.

The ternary operator

To pick one of two values in a single line you use the ternary operator ? :: string m = age >= 18 ? "adult" : "child";.

First the condition, then ?, the value if true, :, and the value if false. It shortens simple two-way assignments; but nesting ternaries hurts readability, so keep them flat.

Ternary and null coalescing

For the case a variable might be null you use the ?? (null coalescing) operator: string name = input ?? "guest";. If input is null, 'guest' is taken.

This is much cleaner than writing input != null ? input : "guest". The ternary is general-purpose, ?? is specialized for null; both save the day for one-line picks.

Exercise Even or odd with the ternary

Declare an n variable with the value 8. Use the ternary operator to produce parity: if n % 2 == 0 then "even", otherwise "odd". Then print parity with Console.WriteLine.

Show example solution

"odd";
Example solution:
using System;

class Program
{
    static void Main()
    {
        int n = 8;
        string parity = n % 2 == 0 ? "even" : "odd";
        Console.WriteLine(parity);
    }
}

Test yourself

Complete the ternary separator

int n = 7;
string parity = (n % 2 == 0) ____ "even" : "odd";

Show answer

int n = 7;
string parity = (n % 2 == 0) ? "even" : "odd";

Match each sign to its use

?

Ternary true branch
:

Ternary false branch
??

Null fallback value
?:

Ternary pair
What is the result of 5 >= 3 ? "a" : "b"?
```
string r = 5 >= 3 ? "a" : "b";
```
- "b"
- "ab"
- "a"
- Compile error
Show answer

"a" — Correct. 5 >= 3 is true, so 'a' is picked.

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The ternary operator