Novice about $coon Connection related issues

Novice connection issues with $coon
For database connections, I've found two types, the first of which are:
$db _host= ' localhost ';?? Database host Name
$db _user= ' root ';? ?? ??? Database user Account
$db _passw= ' 123 ';? ?//Database user password
$db _name= ' list ';? ?? ?? ?//Database specific
$conn = mysql_connect ($db _host, $db _user, $db _passw) or Die (' Database connection failed! ');

The second type is:
$conn = mysql_connect (localhost,root,123) or Die (' Database connection failed! ');

Obviously the second is more convenient than the first one, why some people like to use the first kind of, is not what other uses.
------Solution--------------------
There are no two ways!
Cautious people are reluctant to let others see the password, so the variable is used
Of course, in real code, these variables are placed where you can't see them.
------Solution--------------------
Another explanation is that variables can be placed in a separate configuration file, which is then included so that it is easy to manage later.
------Solution--------------------
Don't be so tangled, it's a habit.

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