simple iOS increment/decrement app multiplication question

Counter is a class, you don't posted the code.
Probably, this line is just an error:

    _byTwoCounter *= 2;   <---- THIS LINE WON'T WORK. I TRIED 'SELF' AS WELL BUT NO DICE

It could work if _byTwoCounter is NSInteger, but in your case it's Counter. Probably class Counter has a property currentCount and so the line could look like:

_byTwoCounter.currentCounter = 2;

Sorry, I didn't post the other code because I figured my error was right there. Here it is

//
//  Counter.h
//  TheCounter

//

#import <Foundation/Foundation.h>

@interface Counter : NSObject

@property (nonatomic) NSInteger currentCount;

// designated initializer
- (id)initWithInitialCount:(NSInteger)initialCount;

- (void)increment;
- (void)decrement;

@end

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//
//  Counter.m
//  TheCounter
//

//

#import "Counter.h"

@implementation Counter

//override the designated init
- (id)initWithInitialCount:(NSInteger)initialCount
{
    //must always be done in designated init
    //convenience inits must call the des init this way
    self = [super init];
    
    if (self)
    {
        //give the instance variables initial values
        self.currentCount = initialCount;
        //[self setCurrentCount:initialCount]; //either way works
    }
    
    return self;
}

//convenience init
- (id)init
{
    return [self initWithInitialCount:0];
}

- (void)increment
{
    self.currentCount++; //access the property setter
    //not the "_currentCount" instance var
}

- (void)decrement
{
    self.currentCount--;
}


@end

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//
//  StepCounter.h
//  TheCounter
//


#import "Counter.h"
 //public
@interface StepCounter : Counter

//instance var
@property (nonatomic, readonly) NSInteger stepAmount;

//designated initializer
- (id)initWithInitialCount:(NSInteger)initialCount
                stepAmount:(NSInteger)stepAmount;

@end

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//
//  StepCounter.m
//  TheCounter
//

//

#import "StepCounter.h"

@implementation StepCounter

- (id)initWithInitialCount:(NSInteger)initialCount stepAmount:(NSInteger)stepAmount
{
    //self = [super init]; rule
    //call super init on my superclass's des init
    self = [super initWithInitialCount:initialCount];
    
    if (self)
    {
        //init instance vars
        _stepAmount = stepAmount; //getter = param
    }
    
    return self;
}




@end

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_byTwoCounter.currentCounter *= 2;

prevents errors now, so thank you for that. However, the logic isn't working.

My intent is is to make the  2x label increment by twice the current count.

And then for the third label I need to increment by 3x the current count. Am I missing something?

I'll add my controller here for you to see as well:

//
//  MVCDemoViewController.h
//  TheCounter
//
//
//

#import <UIKit/UIKit.h>

//public
@interface MVCDemoViewController : UIViewController

@end

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//
//  MVCDemoViewController.m
//  TheCounter
//
//

#import "MVCDemoViewController.h"
#import "Counter.h"

//private
@interface MVCDemoViewController ()

@property (nonatomic) Counter *byOneCounter;
@property (nonatomic) Counter *byTwoCounter;
@property (nonatomic) Counter *byThreeCounter;
@property (weak, nonatomic) IBOutlet UILabel *byOneLabel;
@property (weak, nonatomic) IBOutlet UILabel *byTwoLabel;
@property (weak, nonatomic) IBOutlet UILabel *byThreeLabel;


@end

@implementation MVCDemoViewController

//lazy instatiation always refers to getter
//this is the getter method
- (Counter *)byOneCounter
{
    if(!_byOneCounter) _byOneCounter = [[Counter alloc] initWithInitialCount:0];
    
    return _byOneCounter;
}

- (Counter *)byTwoCounter
{
    if (!_byTwoCounter) _byTwoCounter = [[Counter alloc] initWithInitialCount:0];
    
    _byTwoCounter.currentCount *= 2;
    return _byTwoCounter;
}

- (Counter *)byThreeCounter
{
    if (!_byThreeCounter)
        _byThreeCounter = [[Counter alloc] initWithInitialCount:0];
    
    return _byThreeCounter;
}


//ctrl+dragged increment to the yellow 
//box Demo View Controller
//to connect same for decrement. Connected them up that way
//once that is done, I can now tap and see action happen
- (IBAction)incrementTapped:(UIButton *)sender
{
    //update the byOneCounter instance
    [self.byOneCounter increment]; //byOneCounter.increment
    
    //update the labels
    self.byOneLabel.text = [NSString stringWithFormat:@"%d", self.byOneCounter.currentCount];
    
    self.byTwoLabel.text = [NSString stringWithFormat:@"%d", self.byOneCounter.currentCount];
    
    self.byThreeLabel.text = [NSString stringWithFormat:@"%d", self.byOneCounter.currentCount];

    NSLog(@"increment tapped");
}

- (IBAction)decrementTapped:(UIButton *)sender
{
    //update counter
    [self.byOneCounter decrement];
    
    //update labels
    self.byOneLabel.text = [NSString stringWithFormat:@"%d", self.byOneCounter.currentCount];
    
    self.byTwoLabel.text = [NSString stringWithFormat:@"%d", self.byOneCounter.currentCount];
    
    self.byThreeLabel.text = [NSString stringWithFormat:@"%d", self.byOneCounter.currentCount];
    NSLog(@"decrement tapped");
}



@end

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That's your code for the Increment button:

- (IBAction)incrementTapped:(UIButton *)sender
{
    //update the byOneCounter instance
    [self.byOneCounter increment]; //byOneCounter.increment
    
    //update the labels
    self.byOneLabel.text = [NSString stringWithFormat:@"%d", self.byOneCounter.currentCount];
    
    self.byTwoLabel.text = [NSString stringWithFormat:@"%d", self.byOneCounter.currentCount];
    
    self.byThreeLabel.text = [NSString stringWithFormat:@"%d", self.byOneCounter.currentCount];

    NSLog(@"increment tapped");
}

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In this line:

 [self.byOneCounter increment];

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you call:

- (Counter *)byOneCounter
{
    if(!_byOneCounter) _byOneCounter = [[Counter alloc] initWithInitialCount:0];
    
    return _byOneCounter;
}

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What exactly you wanted to do?

Maybe, you need to increment all three elements? Something like:

[self.byOneCounter increment];
[self.byTwoCounter increment];
[self.byThreeCounter increment];

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Thank you.

when the increment button is clicked I want
 by one counter to return and display
1, then 2, then 3 (each click of incrment)....

then byTwoCounter will also display
return 2, 4,6,8....

then also byThreeCounter displays
3,6,9,12...

just like i have in the picture at the very top

You've been very helpful. Much appreciated :)