Editing Ternary conditional operator (section)

==Result type==
Clearly the type of the result of the {{code|?:}} operator must be in some sense the [[type unification]] of the types of its second and third operands. In C this is accomplished for [[numeric type]]s by [[arithmetic promotion]]; since C does not have a [[type hierarchy]] for [[Pointer (computer programming)|pointer]] types, pointer operands may only be used if they are of the same type (ignoring [[type qualifier]]s) or one is [[void type|void]] or [[Null pointer|NULL]]. It is [[undefined behaviour]] to mix pointer and integral or incompatible pointer types; thus

<syntaxhighlight lang="c">
number = spell_out_numbers ? "forty-two" : 42;
</syntaxhighlight>

will result in a [[compile-time error]] in most compilers.