Editing Ternary conditional operator (section)

===C===
A traditional if-else construct in [[C (programming language)|C]] is written:

<syntaxhighlight lang="c">
if (a > b) {
    result = x;
}
else {
    result = y;
}
</syntaxhighlight>

This can be rewritten as the following statement:

<syntaxhighlight lang="c">
result = a > b ? x : y;
</syntaxhighlight>

As in the if-else construct only one of the expressions 'x' and 'y' is evaluated. This is significant if the evaluation of 'x' or 'y' has [[Side effect (computer science)|side effect]]s.<ref name="ISO/IEC 9899:1999">ISO.IEC 9899:1999 (E) 6.5.15.4</ref> The behaviour is undefined if an attempt is made to use the result of the conditional operator as an [[Value (computer science)#lrvalue|lvalue]].<ref name="ISO/IEC 9899:1999"/>

A [[GNU Project|GNU]] extension to C allows omitting the second operand, and using implicitly the first operand as the second also:

<syntaxhighlight lang="c">
a = x ? : y;
</syntaxhighlight>

The expression is equivalent to

<syntaxhighlight lang="c">
a = x ? x : y;
</syntaxhighlight>

except that expressions ''a'' and ''x'' are evaluated only once. The difference is significant if evaluating the expression has side effects. This shorthand form is sometimes known as the [[Elvis operator]] in other languages.