When you are sure your script is perfectly working, you can get rid of warning and notices like this: Put this line at the beginning of your PHP script:
error_reporting(E_ERROR);
Before that, when working on your script, I would advise you to properly debug your script so that all notice or warning disappear one by one.
So you should first set it as verbose as possible with:
error_reporting(E_ERROR | E_WARNING | E_PARSE | E_NOTICE);
UPDATE: how to log errors instead of displaying them
As suggested in the comments, the better solution is to log errors into a file so only the PHP developer sees the error messages, not the users.
A possible implementation is via the .htaccess file, useful if you don’t have access to the php.ini file (source).
# Suppress PHP errors
php_flag display_startup_errors off
php_flag display_errors off
php_flag html_errors off
php_value docref_root 0
php_value docref_ext 0
# Enable PHP error logging
php_flag log_errors on
php_value error_log /home/path/public_html/domain/PHP_errors.log
# Prevent access to PHP error log
<Files PHP_errors.log>
Order allow,deny
Deny from all
Satisfy All
</Files>