c# - timer application not running properly -

i writing simple c# application, in program counts 15 seconds , outputs "15" 15 seconds have passed. although, program works fine first few trials, starts freeze instead. know why? , how can improve it?

 public void timer()         {             time.text = "restart";             int = 0;             datetime st1 = datetime.now;             string time1 = st1.second.tostring();             int timef = convert.toint32(time1);             int timef2;              while (i < 15)             {                  datetime st2 = datetime.now;                 string time2 = st2.second.tostring();                 timef2 = convert.toint32(time2);                 = timef2 - timef;              }              time.text = i.tostring();             = 0;         } 

you need use timer if want application perform actions after specific amount of time.

system.timers.timer timer = new system.timers.timer(); timer.interval = 15 * 1000; timer.elapsed += timer_elapsed; timer.start(); int timercount=0;  void timer_elapsed(object sender, eventargs e) {  timercount++;  int timeelapsed = timercount * 15; }