elisp to modify snippets in yasnippet

Question

I have this elisp code from yasnippet:

`(progn (goto-char (point-min)) (unless (re-search-forward
"^using\\s-+namespace std;" nil 'no-errer) "std::"))
`cout << $0${1:} << "${2:\n}";

which will print:

cout << ... << "\n"; 

when you type cout and TAB to complete. Note that ... is where my cursor will be.

If I don't have using namespace std in my C++ code, then the insertion becomes:

std:: cout << ... << "\n"; 

Instead of the newline character, \n, I tried to modify so that endl is printed instead. In other words:

cout << ... << endl; 

and

std::cout << ... << std::endl; 

Question How to have std:: inserts at both cout and endl if no using namespace std; is found?

Attempts

I tried the followings, none of them work:

 `(progn (goto-char (point-min)) (unless (re-search-forward
    "^using\\s-+namespace std;" nil 'no-errer) "std::"))
    `cout << $0${1:} << endl;

This only prints std:: to the front, cout if I do not have the using namespace std;.

`(progn (goto-char (point-min)) (unless (re-search-forward
        "^using\\s-+namespace std;" nil 'no-errer) "std::"))
        `cout << $0${1:}
`(progn (goto-char (point-min)) (unless (re-search-forward
        "^using\\s-+namespace std;" nil 'no-errer) "std::"))
        'endl;

This previous code just prints out:

cout << ...
`(progn (goto-char (point-min)) (unless (re-search-forward
            "^using\\s-+namespace std;" nil 'no-errer) "std::"))
            'endl;