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POCalculator app won't add operand to array
 

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  1. POCalculator app won't add operand to array
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    <p>I am trying to make a calculator app, but when I press enter nothing is pushed into the array. I have a class called <code>CaculatorBrain</code> where the <code>pushElement</code> method is defined, however (for now) I defined and implemented <code>pushElement</code> method in the view controller. </p> <p>When I log the operand object as it is typed in the console when enter is pressed the contents of array is nil! Why is that?</p> <pre><code>#import "CalculatorViewController.h" #import "CalculatorBrain.h" @interface CalculatorViewController () @property (nonatomic)BOOL userIntheMiddleOfEnteringText; @property(nonatomic,copy) NSMutableArray* operandStack; @end @implementation CalculatorViewController BOOL userIntheMiddleOfEnteringText; - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib. } -(NSMutableArray*) operandStack { if (_operandStack==nil) { _operandStack=[[NSMutableArray alloc]init]; } return _operandStack; } -(CalculatorBrain*)Brain { if (!_Brain) _Brain= [[CalculatorBrain alloc]init]; return _Brain; } - (IBAction)digitPressed:(UIButton*)sender { if (self.userIntheMiddleOfEnteringText) { NSString *digit= [sender currentTitle]; NSString *currentDisplayText=self.display.text; NSString *newDisplayText= [currentDisplayText stringByAppendingString:digit]; self.display.text=newDisplayText; NSLog(@"IAm in digitPressed method"); } else { NSString *digit=[sender currentTitle]; self.display.text = digit; self. userIntheMiddleOfEnteringText=YES; } } -(void)pushElement:(double)operand { NSNumber *operandObject=[NSNumber numberWithDouble:operand]; [_operandStack addObject:operandObject]; NSLog(@"operandObject is %@",operandObject); NSLog(@"array contents is %@",_operandStack); } - (IBAction)enterPressed { [self pushElement: [self.display.text doubleValue] ]; NSLog(@"the contents of array is %@",_operandStack); userIntheMiddleOfEnteringText= NO; } </code></pre>
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    1. COIt looks like you never actually initialize the operandStack - you're using the variable backing it (`_operandStack`) instead. Try putting your operand stack allocation/initialization in `viewDidLoad`.
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    2. COIndeed, why are you using `_operandStack` instead of `self.operandStack` anywhere outside `-operandStack`? Also, why is that property marked `copy` instead of `strong` (or `retain`)?
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      1. POCalculator app won't add operand to array
      1. USCaleb
    3. COself.operandStack instead of _operandStack did solve the problem, but i am confused my understanding is _operandStack and self.operandStack are both serve as the same purpose meaning that xcode is synthesizing the operandStack for me so both self.operandStack or _operandStack can be used ? can you help me with why self.operandStack solve the problem
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      1. USDina
 

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