Conditional operator

The conditional operator is supported in many programming languages. This term usually refers to ?: as in C, C++, C#, and JavaScript. However, in Java, this term can also refer to && and ||.

&& and ||

In some programming languages, e.g. Java, the term conditional operator refers to short circuit boolean operators && and ||. The second expression is evaluated only when the first expression is not sufficient to determine the value of the whole expression.^[1]

Difference from bitwise operator

& and | are bitwise operators that occur in many programming languages. The major difference is that bitwise operations operate on the individual bits of a binary numeral, whereas conditional operators operate on logical operations. Additionally, expressions before and after a bitwise operator are always evaluated.

if (expression1 || expression2 || expression3)

If expression 1 is true, expressions 2 and 3 are NOT checked.

if (expression1 | expression2 | expression3)

This checks expressions 2 and 3, even if expression 1 is true.

Short circuit operators can reduce run times by avoiding unnecessary calculations. They can also avoid Null Exceptions when expression 1 checks whether an object is valid.

Usage in Java

class ConditionalDemo1 {

    public static void main(String[] args) {
        int value1 = 1;
        int value2 = 2;
        if ((value1 == 1) && (value2 == 2))
            System.out.println("value1 is 1 AND value2 is 2");
        if ((value1 == 1) || (value2 == 1))
            System.out.println("value1 is 1 OR value2 is 1");
    }
}

"?:"

In most programming languages, ?: is called the conditional operator. It is a type of ternary operator. However, ternary operator in most situations refers specifically to ?: because it is the only operator that takes three operands.^[2]

Regular usage of "?:"

?: is used in conditional expressions. Programmers can rewrite an if-then-else expression in a more concise way by using the conditional operator.^[3]

Syntax

condition ? expression 1 : expression 2

condition: An expression which is evaluated as a boolean value.

expression 1, expression 2: Expressions with values of any type.

If the condition is evaluated to true, the expression 1 will be evaluated. If the condition is evaluated to false, the expression 2 will be evaluated.

It should be read as: "If condition is true, assign the value of expression 1 to result. Otherwise, assign the value of expression 2 to result."

Association property

The conditional operator is right-associative, meaning that operations are grouped from right to left. For example, an expression of the form a ? b : c ? d : e is evaluated as a ? b : (c ? d : e).^[2]

Examples by languages

Java

class ConditionalDemo2 {

    public static void main(String[] args) {
        int value1 = 1;
        int value2 = 2;
        int result;
        boolean someCondition = true;
        result = someCondition ? value1 : value2;

        System.out.println(result);
    }
}

In this example, because someCondition is true, this program prints "1" to the screen. Use the ?: operator instead of an if-then-else statement if it makes your code more readable; for example, when the expressions are compact and without side-effects (such as assignments).

C++

#include <iostream>

int main() {
    int x = 1;
    int y = 2;
    std::cout << ( x > y ? x : y ) << " is the greater of the two." << std::endl;
}

There are several rules that apply to the second and third operands in C++:

• If both operands are of the same type, the result is of that type
• If both operands are of arithmetic or enumeration types, the usual arithmetic conversions (covered in Standard Conversions) are performed to convert them to a common type
• If both operands are of pointer types or if one is a pointer type and the other is a constant expression that evaluates to 0, pointer conversions are performed to convert them to a common type
• If both operands are of reference types, reference conversions are performed to convert them to a common type
• If both operands are of type void, the common type is type void
• If both operands are of the same user-defined type, the common type is that type.^[4]

C#

// condition ? first_expression : second_expression;

static double sinc(double x) 
{
    return x != 0.0 ? Math.Sin(x)/x : 1.0;
}

There are several rules that apply to the second and third operands x and y in C#:

• If x has type X and y has type Y:
• If an implicit conversion exists from X to Y but not from Y to X, Y is the type of the conditional expression.
• If an implicit conversion exists from Y to X but not from X to Y, X is the type of the conditional expression.
• Otherwise, no expression type can be determined, and a compile-time error occurs.
• If only one of x and y has a type, and both x and y are implicitly convertible to that type, that type is the type of the conditional expression.
• Otherwise, no expression type can be determined, and a compile-time error occurs.^[2]

JavaScript

var age = 26;
var beverage = (age >= 21) ? "Beer" : "Juice";
console.log(beverage); // "Beer"

The conditional operator of JavaScript is compatible with the following browsers:

Chrome, Edge, Firefox (1), Internet Explorer, Opera, Safari, Android webview, Chrome for Android, Edge Mobile, Firefox for Android (4), Opera for Android, Safari on IOS, Samsung Internet, Node.js.^[5]

Special usage in conditional chain

The ternary operator is right-associative, which means it can be "chained" in the following way, similar to an if ... else if ... else if ... else chain.^[4]

Examples by languages

JavaScript

function example(…) {
   		 return condition1 ? value1
        		: condition2 ? value2
         		: condition3 ? value3
         		: value4;
}

// Equivalent to:

function example(…) {
    	if (condition1) { return value1; }
  		else if (condition2) { return value2; }
   		else if (condition3) { return value3; }
    	else { return value4; }
}

C/C++

const double a =
	expression1	? a1
	: expression2	? a2
	: expression3	? a3
	: /*otherwise*/	a4;

// Equivalent to:

double a;
  if (expression1)
	a = a1;
  else if (expression2)
	a = a2;
  else if (expression3)
	a = a3;
  else /*otherwise*/
	a = a4;

Special usage in assignment expression

the conditional operator can yield a L-value in C/C++ which can be assigned another value, but the vast majority of programmers consider this extremely poor style, if only because of the technique's obscurity.^[6]

C/C++

((foo) ? bar : baz) = frink;

//equivalent to:
 if (foo)
		bar = frink;
 else
		baz = frink;

See also

• ?:, a conditional operator in computer programming
• Ternary operation
• Bitwise operators
• short circuit boolean operators
• Operator (programming)

References

1. "Equality, Relational, and Conditional Operators (The Java™ Tutorials > Learning the Java Language > Language Basics)". docs.oracle.com. Retrieved 2019-04-29.
2. BillWagner. "?: Operator - C# Reference". docs.microsoft.com. Retrieved 2019-04-29.
3. "The ? : operator in Java". www.cafeaulait.org. Retrieved 2019-04-29.
4. mikeblome. "Conditional Operator: ?". docs.microsoft.com. Retrieved 2019-04-29.
5. "Conditional (ternary) operator - JavaScript". developer.mozilla.org. Retrieved 2019-04-29.
6. "Conditional Operator". wiki.c2.com. Retrieved 2019-04-29.