8 Statements [stmt.stmt]

8.3 Expression statement [stmt.expr]

Expression statements have the form
The expression is a discarded-value expression.
All side effects from an expression statement are completed before the next statement is executed.
An expression statement with the expression missing is called a null statement.
[Note 1: 
Most statements are expression statements — usually assignments or function calls.
A null statement is useful to supply a null body to an iteration statement such as a while statement ([stmt.while]).
— end note]