I have a function which returns the pictures for 2 type of devices. In function(response) i get the value correctly, then autside of $.post section the value is undefined.

function findHeadShot(key) {
          var tip;
          var ajaxUrl = "gettip.php";
          var data = { action: 'function1', azon: key};
              $.post(ajaxUrl, data, function(response) {
                  tip = response; //Here i get the response, and it is fine yet
              });
              alert(tip);         //Here the response is undefined, but why?
              switch (tip) {
                case "pc":
                   return "pc_icon.png";
                  break;

                case "server":
                   return "server_icon.png";
                  break;
              
                default:
                  return "server_icon.png";
                  break;
              }
      }