Back to the future 2qvod in-depth understanding of php41--back to the future

For those readers who are unfamiliar with this concept, a loop is a control structure that allows you to reuse the same series of PHP commands over and over again. The actual number of repetitions can be decided by you.
　The first and simplest loop is the so-called "while" loop, as shown below:
while (condition)
{
do this!
}
Or, in Chinese,
while (it’s raining)
{
Bring an umbrella!
}
　 In this case, as long as the value of the condition is true, remember what you learned last time? --- The PHP commands in curly brackets will always be executed. As soon as the condition becomes false - for example, in the above example, the sun comes out, the loop will terminate and subsequent commands will not be executed.
　 Here is a simple example to illustrate how to use a "while" loop:
< ?
// If the form has not been submitted yet, display the initialization page
if (!$submit)
{
?>
< html>
< head>
< /head>
< body>
< h2>Incredibly wonderful time machine (time machine)< /h2>
< form action="tmachine.php " method="POST">
In which year do you plan to visit?
< input type="text" name="year" size="4" maxlength="4">
< input type=" submit" name="submit" value="Go">
< /form>
< /body>
< /html>
< ?
}
else
// Otherwise, it will be processed and generated A new page
{
?>
< html>
< head>
< /head>
< body>
< ?
// The current year
$current = 2001;
// Check the future time and generate the corresponding information
In this example, we first ask the user for the year he wishes to access - the year is stored in the variable year and passed to the PHP script.
　The script first checks the year to make sure it is in the past [haha, we seem to be doing these things ourselves now] and then uses a "while" loop to calculate backwards from the current year - 2001 and store the result in the variable current until Until the values ​​of $current and $year are the same.
Please note that we use the submit variable to generate both an initialization form and a processing page on the same PHP page - we have explained this technology to you in detail last time.​

The above introduces Back to the Future 2qvod and an in-depth understanding of php41-Back to the Future, including the content of Back to the Future 2qvod. I hope it will be helpful to friends who are interested in PHP tutorials.