TimeCounter.m

#import "ViewController.h"

@interface ViewController (){
    
    IBOutlet UILabel *lblTime;
    NSTimer *timer;
    NSUInteger timerCount;
}


@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    timerCount = 0;
    lblTime.text = @"0";
}

-(void)count{
    timerCount++;
    lblTime.text = [NSString stringWithFormat:@"%lu", (unsigned long)timerCount];
}

- (IBAction)btnStart:(id)sender {
    timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(count) userInfo:nil repeats:YES];
}

- (IBAction)btnStop:(id)sender {
    [timer invalidate];
    timer = nil;
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


@end