[ iOS ] How to create a Stopwatch

ViewController.m

//
//  ViewController.m
//  stopwatch
//
  
#import "ViewController.h"
  
@interface ViewController ()
@end
  
@implementation ViewController
@synthesize timerLabel,startBtn,resetBtn;
  
- (void)viewDidLoad {
    [super viewDidLoad];
     
    running = NO;
    count = 0;
    timerLabel.text = @"00:00.00";
     
    startBtn.layer.cornerRadius = 45;
    resetBtn.layer.cornerRadius = 45;
     
}
  
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
  
- (IBAction)startBtnPushed:(id)sender {
     
    if (running == NO) {
        running = YES;
        [startBtn setTitle:@"STOP" forState:UIControlStateNormal];
         
        if (myTimer == nil) {
            myTimer = [NSTimer scheduledTimerWithTimeInterval:0.01 target:self selector:@selector(updateTimer) userInfo:nil repeats:YES];
        }
         
    } else {
        [self stopTimer];
    }
}
  
- (IBAction)resetBtnPushed:(id)sender {
    [self stopTimer]; 
    count = 0;
    timerLabel.text = @"00:00.00";
}
  
- (void)stopTimer {
    running = NO;
    [myTimer invalidate];
    myTimer = nil;
    [startBtn setTitle:@"START" forState:UIControlStateNormal];
}
  
- (void)updateTimer {
    count++;
     
    int min = floor(count/100/60);
    int sec = floor(count/100);
    int mSec = count % 100;
     
    if (sec >= 60) {
        sec = sec % 60;
    }
     
    timerLabel.text = [NSString stringWithFormat:@"%02d:%02d.%02d",min,sec,mSec];
}
  
@end