Deep understanding of PHP4 (1)--back to the future

For those of you who are unfamiliar with this concept, loops are a control structure that allows you to reuse a series of PHP commands over and over again. The actual number of repetitions can be determined by yourself.

The first, and simplest, loop is the so-called "while" loop, as follows:

while (condition)
{
Do this!
}

Or, in Chinese,

while (it rained)
{
Take the Umbrella!
}

In this case, as long as the value of the condition is true, remember how the last time you learned it?---the PHP command in brackets will always execute. As long as the condition becomes false-for example, in the example above, the sun comes out, the loop terminates, and the subsequent commands are no longer executed.

Here is a simple example of how to use the "while" Loop:



<?

Displays the initialization page if the form has not yet been submitted
if (! $submit)
{
?>

< html>

< head>

< body>
< h2> incredibly wonderful Time Machine (Times machine) < form action= "tmachine.php" method= "POST" >
Which year would you like to visit?
< input type= "text" name= "Year" size= "4" maxlength= "4" >
< input type= "submit" name= "submit" value= "Go" >
</form>
</body>

<?
}
Else
Otherwise, it is processed and a new page is generated
{
?>

< html>

< head>

< body>

<?
The current year
$current = 2001;

Check the future time and generate the appropriate information


In this example, we first ask the user about the year that he wants to visit-the year is stored in the yearly variable and sent to the PHP script.

The script first checks the year to confirm that it was in the past [hehe, we're doing these things now.] Then use a "while" loop to calculate the result from the current year-2001 backwards, until the values of $current and $year are the same.

Note that we have used the submit variable to make the same PHP page produce both the initialization form and the processing page-the technique we have explained to you last time.