var stars = 0;    

$("#submit").click(function(){
    function_final();

    if (stars != 0){
        return true;
    }
    alert("Please, select the stars and thank you for valuing us.");
});

function function_final(){
    if (stars != 0)
        return true;

    return false;
}

function change_stars(value){
    stars = value;
}