value get released from variable when value is float number

Question

I am facing such strange issue right now, I am trying to implement calculator in my project the demo. The place I want to implement is ARC enable and my project ARC disable everything is working perfectly in that demo its working perfect in my project tOO but when i try to do operation on float values then my application crashes says EXC_BAD_ACCESS(code 1.... below is my code

_currentValue and _previousValue are like this in .h file

@property (retain,nonatomic) NSNumber* currentValue;  
@property (retain,nonatomic) NSNumber* previousValue;

in my .m file there are 2 methods where i face problem

- (NSString *)calculateValueToString:(NSString *)valueString ForType:(enum State)type{

    _currentValue = [numberFormatterFormal numberFromString:valueString];

    NSLog(@"%@",_currentValue);  //whatever number i input it get prints here

    [self calculateValue]; // this method get called
    state = type;          

    if (state != Equal){
        _previousValue = _currentValue;
         NSLog(@"%@",_previousValue);  // get print 
        _currentValue = @0 ;
    }

     NSLog(@"_previousValue%@",_previousValue);   // get print 
    NSLog(@"_currentValue%@",_currentValue);      // get print
    return [numberFormatterFormal stringFromNumber:_currentValue]; 
}

- (void)calculateValue{ 

    switch (state) { 
        case Plus:
            _currentValue = [NSNumber numberWithDouble:[_previousValue doubleValue] + [_currentValue doubleValue]];
            break;
        case Minus:                        //GET ONLY EXECUTE ONLY IF OPERATION IS -

              NSLog(@"%@",_currentValue);  // it has value 

   --->>>>>>> HERE APP CRASH         NSLog(@"%@",_previousValue);   // app crashes here

            _currentValue = [NSNumber numberWithDouble:[_previousValue doubleValue] - [_currentValue doubleValue]];

               NSLog(@"%@",_currentValue);  
              // THIS ALL WORK PERFECTLY IN THAT DEMO WHICH IS ARC ENABLE 
            break;
        case Multiple:
            _currentValue = [NSNumber numberWithDouble:[_previousValue doubleValue] * [_currentValue doubleValue]];
            break;
        case Divide:
            _currentValue = [NSNumber numberWithDouble:[_previousValue doubleValue] / [_currentValue doubleValue]];
            break;
        default:
            break;
    }
}

Answer 1

You're accessing your instance variables directly, and using manual reference counting. This isn't going to work.

All of the memory management is done in the synthesised accessor methods, so you must use the property accessors, e.g:

self.currentValue = ....;

Never

_currentValue = ...;

Or you will be bypassing all of the retain / release calls that the accessors are doing for you.