How to use the ?: conditional operator in C#?

The conditional operator (also called the ternary operator) is represented by the symbol ?:. It provides a concise way to write simple if-else statements in a single expression. The operator has right-to-left associativity and evaluates a boolean condition to return one of two possible values.

Syntax

Following is the syntax for the conditional operator −

condition ? value_if_true : value_if_false

Where:

• condition is an expression that evaluates to a boolean value

• value_if_true is returned if the condition is true

• value_if_false is returned if the condition is false

How It Works

The conditional operator works as follows −

• The first operand (condition) is implicitly converted to bool.

• If the condition evaluates to true, the second operand is evaluated and returned.

• If the condition evaluates to false, the third operand is evaluated and returned.

Remember, only one of the last two operands is evaluated in a conditional expression.

Using Conditional Operator for Simple Assignment

Example

using System;

class Program {
    static void Main(string[] args) {
        int num1 = 100, num2;
        num2 = (num1 == 100 ? 200 : 0);
        Console.WriteLine("Number One = " + num1);
        Console.WriteLine("Number Two = " + num2);
    }
}

The output of the above code is −

Number One = 100
Number Two = 200

Using Conditional Operator for String Messages

Example

using System;

class Program {
    static void Main(string[] args) {
        int score = 85;
        string result = (score >= 60 ? "Pass" : "Fail");
        Console.WriteLine("Score: " + score);
        Console.WriteLine("Result: " + result);
        
        int age = 17;
        string eligibility = (age >= 18 ? "Eligible to vote" : "Not eligible to vote");
        Console.WriteLine("Age: " + age);
        Console.WriteLine(eligibility);
    }
}

The output of the above code is −

Score: 85
Result: Pass
Age: 17
Not eligible to vote

Nested Conditional Operators

Example

using System;

class Program {
    static void Main(string[] args) {
        int marks = 92;
        string grade = (marks >= 90 ? "A" : marks >= 80 ? "B" : marks >= 70 ? "C" : "D");
        Console.WriteLine("Marks: " + marks);
        Console.WriteLine("Grade: " + grade);
        
        int temperature = 25;
        string weather = (temperature > 30 ? "Hot" : temperature > 20 ? "Warm" : "Cold");
        Console.WriteLine("Temperature: " + temperature + "°C");
        Console.WriteLine("Weather: " + weather);
    }
}

The output of the above code is −

Marks: 92
Grade: A
Temperature: 25°C
Weather: Warm

Comparison with If-Else Statement

Conclusion

The conditional operator ?: in C# provides a compact way to write simple conditional expressions. It evaluates a boolean condition and returns one of two values based on the result. Use it for simple assignments and avoid complex nested conditions for better readability.