A while loop just looks at a short comparison and repeats until the comparison is no longer True.

1. The while loop

The while loops don't necessarily use a variable to count. Instead, they execute as long as a condition is True. In fact, if the condition starts out as false, the statements won’t execute at all.

The while statement includes the condition in parentheses, and it is followed by a block of statements within braces. Here is its syntax:
while (condition) {
  code to be executed
}
Here's the earlier example, from the "for" instruction, this version use the "while" loop.
<script type="text/javascript"><!--
var i = 0;
while (i<5) {
  document.write("<br /> i = "+i);
  i++;
}
--></script>
- First it's declared a variable "i" with the value of 0. The "while" statement checks the condition (here i<5), which it's True and permits the execution of block code inside the brackets. The "i++" increments the value of "i" and check again the condition. The loop will stop when the "i" reach 5.
- This script displays the following results:
i = 0
i = 1
i = 2
i = 3
i = 4

2. do ... while loops

The do...while loop is a variant of the "while" loop. First will be executed the block of code, and then it will repeat the loop as long as the specified condition is true.

The syntax is:
do {
  code to be executed
}
while (condition)
Here is a simple example:
<script type="text/javascript"><!--
var x = 8;
do {
  document.write("<br /> x = "+x);
  x++;
}
while (x<5)
--></script>
- This example display "x = 8".
As you can notice, although the condition is false (x<5), the code of braces is still executed once.

Daily Test with Code Example

HTML
CSS
JavaScript
PHP-MySQL
Which attribute is used in <a> tag for the address of the link?
src href rel
<a href="http://coursesweb.net/" title="CoursesWeb.net">CoursesWeb.net</a>
Which CSS property sets the type of the text font?
font-family text-decoration font-size
h2 {
  font-family:"Calibri",sans-serif;
}
What instruction selects all the <div> tags with class="cls"?
querySelector("div.cls") getElementsByTagName("div") querySelectorAll("div.cls")
var elm_list = document.querySelectorAll("div.cls");
var nr_elms = elm_list.length;       // number of selected items
alert(nr_elms);
Indicate the function that can be used to get the sum of values in an array.
array_sum() array_diff() array_shift()
$arr = array(1, 2, 3, 4);
$arr_sum = array_sum($arr);
echo $arr_sum;       // 10
While loops

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