[Undefinedvariable] Notice: Undefinedvariable solution

[Undefinedvariable] Notice: Undefinedvariable error prompt: Notice: & nbsp; Undefined & nbsp; variable: & nbsp; yan_zheng_shu & nbsp; in code: $ yan_zheng_shu & nbsp ;. & nbsp; dechex (mt_rand (1, & nbsp; 15); ". ", but the result is normal. [Undefined variable] Notice: Undefined variable
Error message: Notice: Undefined variable: yan_zheng_shu in
Code:

$yan_zheng_shu .= dechex(mt_rand(1, 15));

". =" Indicates an error, but the result is displayed normally. "+ =" indicates that "=" is okay.

What should I do? After php. ini is installed, the error prompt is disabled?

Or should I give it an empty character before ". =?

Or is "@" added before?

Which method is standardized?

Thank you.


------ Solution --------------------

This post was last edited by xuzuning at 09:40:09, January 24 ,.

Assign an initial value to $ yan_zheng_shu.
$ Yan_zheng_shu = '';
$ Yan_zheng_shu. = dechex (mt_rand (1, 15 ));
------ Solution --------------------
PHP does not need to declare variables,
However, an error at the E_NOTICE level will still be generated.

$yan_zheng_shu .= dechex(mt_rand(1, 15));

Equivalent

$yan_zheng_shu = $yan_zheng_shu . dechex(mt_rand(1, 15));

Obviously not defined

It is necessary to develop good habits.
------ Solution --------------------
Do you know the meaning of. =? the value assignment is from right to left, so this section certainly does not define the previous variable.