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?: Operator (C# Reference)

Visual Studio 2005

The conditional operator (?:) returns one of two values depending on the value of a Boolean expression. The conditional operator is of the form

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condition ? first_expression : second_expression;

If condition is true, first expression is evaluated and becomes the result; if false, the second expression is evaluated and becomes the result. Only one of two expressions is ever evaluated.

Calculations that might otherwise require an if-else construction can be expressed more concisely and elegantly with the conditional operator. For example, to avoid a division by zero in the calculation of the sin function you could write either

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if(x != 0.0) s = Math.Sin(x)/x; else s = 1.0;

or, using the conditional operator,

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s = x != 0.0 ? Math.Sin(x)/x : 1.0;

The conditional operator is right-associative, so an expression of the form

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a ? b : c ? d : e

is evaluated as

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a ? b : (c ? d : e)

not

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(a ? b : c) ? d : e

The conditional operator cannot be overloaded.

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// cs_operator_conditional.cs
using System;
class MainClass
{
    static double sinc(double x) 
    {
        return x != 0.0 ? Math.Sin(x)/x : 1.0;
    }

    static void Main() 
    {
        Console.WriteLine(sinc(0.2));
        Console.WriteLine(sinc(0.1));
        Console.WriteLine(sinc(0.0));
    }
}
 
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Example for those who stopped at algebra
Here's an example for those who do not know sines and cosines, since that should not be a prerequisite for understanding the conditional operator:

int a,b;
string result;
a = Int16.Parse(TextBox1.Text);
b = Int16.Parse(TextBox2.Text);

// result = conditional test ? if true : if false;
result = a > b ? "a is larger" : "a is not larger";


Edit by SJ at MSFT: You can also get a simpler example in the current version of the topic, here: http://msdn.microsoft.com/en-us/library/ty67wk28.aspx.
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Null Check
To check for null using the ?: operator

ValueToCheck == null ? ValueIfNull : ValueIfNotNull;

Sample:

var value = ViewState["AValue"];
MyTextbox.Text = (value != null) ? value .ToString() : String.Empty;
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Example - Minimum-Maximum range restriction
//Perform a Minimum/Maximum comparision to restrict a value to a range
//Set our minimum and maximum limit values
int Min = 0;
int Max = 100;
//Perform three comparisons. One with value below the minimum, one with Value above the maximum
//and one with Value between the minimum and maximum
int A = MinMax(-2, Min, Max);
int B = MinMax(102, Min, Max);
int C = MinMax(25, Min, Max);
//Display the results
Console.WriteLine("Value of A: {0}", A, B, C);
Console.WriteLine("Value of B: {1}", A, B, C);
Console.WriteLine("Value of C: {2}", A, B, C);

private static int MinMax(int Value, int MinVal, int MaxVal)
{
    //if Value is < MinVal, MinVal is returned.
    //if Value is >= MinVal, compare Value to MaxVal
    //  if Value is > MaxVal, MaxVal is returned
    //  if Value is <= MaxVal, Value is returned
    return Value < MinVal ? MinVal : (Value > MaxVal ? MaxVal : Value);
}

//Output
//Value of A: 0
//Value of B: 100
//Value of C: 25
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