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In this C# tutorial, we are going to discuss another important operator, the conditional operator. The conditional operator is named so because it returns a value by evaluating a boolean condition. The conditional operator is also called ternary operator because it has three operands, such as:

• Boolean-condition.
• First expression.
• Second expression.

Syntax of conditional operator -

boolean-condition ? first expression : second expression;

Rules of conditional operator -



• If the result of boolean-condition is true, first expression will be executed and its value is returned.
• If the result of boolean-condition is false, second expression will be executed and its value is returned.
• First expression and second expression must result in a value.

An example of conditional operator

//C# Conditional Operator Example

using System;

class A
{
public static void Main()
{
	//Local variables
	int a=10, b=20;

	
	//A conditional expression with int expressions
	int result1 =a>b ? 10 : 20;
	Console.WriteLine("Result1 is : " + result1);


	//A conditional expression with an int and a double expression, 
	//hence result of condition expression should be stored in a double
	double result2 = a>b ? 10 : 100.50;
	Console.WriteLine("Result2 is : " + result2);
	

	//A conditional expression with char expressions
	char ch = a>b ? 'y' : 'n';
	Console.WriteLine("Result3 is : " + ch);
	

	//A conditional expression with int expression
	result1 = 100>=99 ? 100 : 99;
	Console.WriteLine("Result4 is : " + result1);
}
}

Output

Result1 is 20
Result2 is 100.5
Result3 is n
Result4 is 100

The first expression of conditional operator cannot be left blank

//C# The first expression of conditional operator cannot be left blank

using System;

class A
{
public static void Main()
{
	//Local variables
	int a=10, b=20;

	int result = a>b ? 0 : 10;
	Console.WriteLine("Result1 is : " + result);

	//Intentionally leaving the first expression of the conditional operator 
	//This will throw a compile error.
	char ch = a<b ? : 'n'; 	
	Console.WriteLine("Result2 is : " + ch);
}
}

Compile Error:

A.cs(16,18): error CS1525: Invalid expression term ':'

In the last code, we have intentionally left out the first expression and a compile error has been reported.

The second expression of conditional operator cannot be left blank either

Not specifying the second expression also results in a compile error.

//C# The second expression of conditional operator cannot be left blank either

using System;

class A
{
public static void Main()
{
	//A conditional expression with the missing second expression
	result = 9<2 ? 9 : ;
	
	Console.WriteLine("Result2 is : " + result);
}
}

Output-

A.cs(10,21): error CS1525: Invalid expression term ';'

In the last code, we have intentionally left out the second expression and the compiler has thrown an error, therefore, neither the first, nor the second expression of the conditional operator can be left out.

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An expression of conditional operator can even be a method call.

Any expression(either the first or the second expression) of a conditional operator could even be a method call, but this method call must return a value.

//C# An expression of conditional operator can be a method call, which must return a value.

using System;

class A
{
public char fun()
{
	return 'y';
}

public static void Main()
{
	//Creating an object of class A	
	A ob = new A();

	// Calling function fun() in the first expression of a conditional expression
	char result = 100>99? ob.fun() : 'n'; 

	//Printing the value returned by the conditional expression
	Console.WriteLine("Result is " + result);
}
}

Output-

Result is y

In the last code, the first expression of the conditional operator is a call to a method fun(), which has returned a char value, y.

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