How to delete a cookie?

Is my function of creating a cookie correct? How do I delete the cookie at the beginning of my program? is there a simple coding?

function createCookie(name,value,days)

function setCookie(c_name,value,1) {
  document.cookie = c_name + "=" +escape(value);
}

setCookie('cookie_name',mac);

function eraseCookie(c_name) {
  createCookie(cookie_name,"",-1);
}