I'm also able to call $_GET["s"] with get_search_query() which results a string.

I attempted lots of codes which were designed to work but none of them did. Most give true whatever I actually do. Is not there an easy method of doing this? Thanks

Presuming you mean the literal string "++++"...

if (strpos($_GET['s'], '++++') !== false) {
    // there, do something
} else {
    // not there, do something else
}

Reference: http://php.net/strpos

if( strpos( $_GET['s'], '++++' ) !== false ) {
    // has
} else {
    // doesn't have
}

I am unsure quite what's on your mind, or maybe I am misunderstanding the question, but surely [cde] is the thing you need:

strpos


Edited to repair 'strpos' (nee 'strpoa') typo...oops! Many thanks @Jonah Bron =)