While迴圈

循环结构
do-while循环
while循环
for循环
foreach循环
死循环

在程式語言中，While迴圈（英語：while loop）是一種控制流程的陳述。利用一個返回結果為布林值(Boolean)的表達式作為循環條件，當這個表達式的返回值為“真”(true)時，則反覆執行迴圈內的程式碼；若表達式的返回值為“假”(false)，則結束執行迴圈內的代碼，繼續執行迴圈下面的代碼。

因為While迴圈在區塊內代碼被執行之前，先檢查陳述是否成立，因此這種控制流程通常被稱為是一種前測試迴圈(pre-test loop)。相對而言Do While迴圈，是在迴圈區塊執行結束之後，再去檢查陳述是否成立，被稱為是後測試迴圈。

程式範例

while 迴圈

VB

'這是一個用While迴圈的例子
dim counter as Integer
dim Tick as Integer
counter=5
tick=1
Print "Start"
while counter>0
counter=counter-tick
'迴圈語句
Wend
Print "End"


C/C++

unsigned int counter = 5;
unsigned long factorial = 1;

while (counter > 0)
{
  factorial *= counter--;    /*當滿足迴圈條件（本例為：counter > 0）時會反覆執行該條語句 */
} 

printf("%lu", factorial);


Java

public static void main(str args[]){
    while true{
        System.out.println("Hello World!") //因為條件已經固定為常量true，所以就會不斷執行迴圈內的語句
    }
    int counter = 0 ;
    while counter<5{
        System.out.println("已經運行了"+counter+"次")  //因為條件限定為counter不大於5，所以在counter不大於5的情況下會不斷重複迴圈中的内容
        counter++;
    }
}


Python語言

a = 0
while a <= 10 :   #如果a沒有大於10就執行
    a = a+1
    print(a)


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