迭代语句为 while，while，do-while 循环

迭代声明/循环分为两类：

• 头控迭代语句/循环
• 脚控迭代语句/循环

头控可控的迭代声明/循环

for ([<expression>]; [<expression>]; [<expression>]) <statement>
while (<expression>) <statement>

Version >= C99

for ([declaration expression]; [expression] [; [expression]]) statement

脚控迭代声明/循环

do <statement> while (<expression>);