Reinitialization problem of string in iPhone

I am making a program and i have to init开发者_如何学编程ialize and reinitialize my NSString variable.I wrote related code but when am trying to reinitialize my NSString variable my program is being crashed. My macdelegate.h file are listed here.

@interface MacCalculatorAppDelegate : NSObject <UIApplicationDelegate> {

    UIWindow *window;

    UIButton *digitPressed;

    UIButton *operatorPressed;

    NSString *waitingOperation;
}
@property (nonatomic, retain) IBOutlet UIWindow *window;

@property ( retain) NSString* waitingOperation;

-(IBAction) digitPressed:(UIButton *)sender;

-(IBAction) operatorPressed:(UIButton *)sender;

@end

And part of code of my macdelegate.m file are listed here.

- (id) init 

    {

    if (self = [super init])
        {

       self.waitingOperation=@"not set";//@"not set";           

        }

        return self;

    }


-(IBAction) digitPressed:(UIButton *)sender {

if(![@"not set" isEqualToString:waitingOperation])

    {
 waitingOperation=@"not set";//@"not set";

}
}

-(IBAction) operatorPressed:(UIButton *)sender {

    NSString *operand=[[sender titleLabel] text];

    resultDisplay.text=operand;

    if([@"+" isEqualToString:operand])

    {    

 waitingOperation=@"+";//@"not set";        

    }

}

- (void)dealloc {

    [waitingOperation release];

    [window release];

    [super dealloc];

}

My all listed codes are above when i am running my program first time this is initialize well but when i am trying to reinitialize my program is doing nothing i suppose this is being crashed. I am new with Objective-C help me.

Thanks in advance.

I think, you have forgotten synthesize statement for your retaining variable waitingOperation and using it as self.waitingOperation would cause a crash, because run time system could not find a setter function for the property waitingOperation

Add @synthesize waitingOperation; in your implementation file.

Use the modified code let me know if you still get the crash.

-(IBAction) digitPressed:(UIButton *)sender 
 {
    if(![ self.waitingOperation isEqualToString:@"not set"])
    {
     self.waitingOperation=@"not set";//@"not set";
   }
}

-(IBAction) operatorPressed:(UIButton *)sender {

    NSString *operand=[[sender titleLabel] text];

    resultDisplay.text=operand;

    if([operand isEqualToString:@"+"])
    {    

      self.waitingOperation=@"+";//@"not set";        
    }

}