8 Statements [stmt.stmt]

8.6 Iteration statements [stmt.iter]

8.6.1 General [stmt.iter.general]

Iteration statements specify looping.
[Note 1: 
An init-statement ends with a semicolon.
— end note]
The substatement in an iteration-statement implicitly defines a block scope which is entered and exited each time through the loop.
If the substatement in an iteration-statement is a single statement and not a compound-statement, it is as if it was rewritten to be a compound-statement containing the original statement.
[Example 1: 
while (--x >= 0) int i; can be equivalently rewritten as while (--x >= 0) { int i; }
Thus after the while statement, i is no longer in scope.
— end example]
A trivially empty iteration statement is an iteration statement matching one of the following forms: The controlling expression of a trivially empty iteration statement is the expression of a while, do, or for statement (or true, if the for statement has no expression).
A trivial infinite loop is a trivially empty iteration statement for which the converted controlling expression is a constant expression, when interpreted as a constant-expression ([expr.const]), and evaluates to true.
The statement of a trivial infinite loop is replaced with a call to the function std​::​this_thread​::​yield ([thread.thread.this]); it is implementation-defined whether this replacement occurs on freestanding implementations.
[Note 2: 
In a freestanding environment, concurrent forward progress is not guaranteed; such systems therefore require explicit cooperation.
A call to yield can add implicit cooperation where none is otherwise intended.
— end note]