Question

Here’s the code

In the .h…

@interface Calculator2ViewController : UIViewController {

    NSString *currentNumber;
    bool buildingNumber;
    NSMutableArray *arrayExpression;
    IBOutlet UILabel *display;

}

In the .m…

-(NSString *) makeCurrentNumber{

    if(!currentNumber){
        currentNumber = [[NSString alloc] init];
        currentNumber = @"";
    }
    NSLog(@"Inside make makeCurrentNumber. The currentNumber is %@",currentNumber);
    return currentNumber;
}



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

    NSString *digit = sender.titleLabel.text;
    NSLog(@"The digit is: %@", digit);
    if(!currentNumber)
      currentNumber = @"";
     currentNumber = [currentNumber stringByAppendingString:digit];
        NSLog (@"The string is: %@",currentNumber);
    buildingNumber = YES;
    }//end of digitPressed

Why does my program crash after 3 appends?

Answer 1

currentNumber initially is retained by the alloc-init in makeCurrentNumber. Later on, you are replacing its value with a auto retained value (the result from stringByAppendingString. Enhance that line with a retain and you might get better results.

[...]
if(!currentNumber)
{
    [self makeCurrentNumber];
}
currentNumber = [[currentNumber stringByAppendingString:digit] retain];
NSLog (@"The string is: %@",currentNumber);
[...]