Which function definition will run correctly?

$1)$ int sum$($int $a,$ int b$)$ return $(a+b)$

$2)$ int sum$($int $a,$ int b$)$ return $(a+b)$;

$3)$ int ${\displaystyle \underset{?}{\overset{?}{}}}(a,b)$ return $(a+b)$

$4)$ none of the mentioned