View source for Template:cpp/language/condition

===Condition===
A {{spar|condition}} can either be an {{rlp|expressions|expression}} or a {{rlpsd|declarations#Simple declaration}}.
{{rrev|since=c++26|
* If it can be syntactically resolved as a {{rlp|structured binding}} declaration, it is interpreted as a structured binding declaration.
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* If it can be syntactically resolved as an expression, it is treated as an expression. Otherwise, it is treated as a declaration{{rev inl|since=c++26| that is not a structured binding declaration}}.

When control reaches condition, the condition will yield a value, which is used to {{{usage|}}}.

====Expression====
If {{spar|condition}} is an expression, the value it yields is the the value of the {{#ifeq: {{{bool|}}}|yes|expression contextually converted to {{c/core|bool}}. If that conversion is ill-formed, the program is ill-formed|expression}}.

====Declaration====
If {{spar|condition}} is a simple declaration, the value it yields is the value of the {{#ifeq: {{{bool|}}}|yes|decision variable (see below) contextually converted to {{c/core|bool}}. If that conversion is ill-formed, the program is ill-formed|decision variable (see below)}}.

=====Non-structured binding declaration=====
The declaration has the following restrictions:
* Syntactically conforms to the following form:
{{rrev multi
|rev1=
:* {{spar|type-specifier-seq}} {{spar|declarator}} {{ttb|{{=}}}} {{spar|assignment-expression}}
|since2=c++11|rev2=
:* {{spar|attribute-specifier-seq}}{{mark optional}} {{spar|decl-specifier-seq}} {{spar|declarator}} {{spar|brace-or-equal-initializer}}
}}
* The declarator cannot specify a {{rlp|function}} or an {{rlp|array}}.
* The {{rev inl|until=c++11|{{rlp|declarations#Specifiers|type specifier sequence}}}}{{rev inl|since=c++11|{{rlp|declarations#Specifiers|declaration specifier sequence}} can only contain type specifiers and {{c/core|constexpr}}, and it}} cannot define a {{rlp|class}} or {{rlp|enum|enumeration}}.

The decision varaiable of the declaration is the declared variable.

{{rrev|since=c++26|
=====Structured binding declaration=====
The declaration has the following restrictions:
* The {{spar|expression}} in its {{rlp|initialization|initializer}} cannot be of an array type.
* The {{rlp|declarations#Specifiers|declaration specifier sequence}} can only contain type specifiers and {{c/core|constexpr}}.

The decision variable of the declaration is the invented variable {{c|e}} {{rlp|structured binding|introduced by the declaration}}.
}}