迭代語句為 while，while，do-while 迴圈

迭代宣告/迴圈分為兩類：

• 頭控迭代語句/迴圈
• 腳控迭代語句/迴圈

頭控可控的迭代宣告/迴圈

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

Version >= C99

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

腳控迭代宣告/迴圈

do <statement> while (<expression>);