sometimes crash EXC_BAD_ACCESS with no message (set NSZombieEnabled)
int currPower = [[powers objectAtIndex:i] intValue];
  int prevPower = [[powers objectAtIndex:i - 1] intValue];

powers = [[NSMutableArray alloc] initWithCapacity:POWER_ARRAY_SIZE];

- (void)dealloc {
     [powers release];
     [super dealloc];
  }

- (void)drawRect:(CGRect)rect
  {
     ...//Do Something
     ...//Check "endindex" and "startindex" not to exceed boundary

     for (int i = endindex; i > startindex; i-=1)
     {

        int currPower = [[powers objectAtIndex:i] intValue];
        int prevPower = [[powers objectAtIndex:i - 1] intValue];

        ...//Doing something

     }
  }

- (void)setPower:(int)p
  {

     [powers addObject:[NSNumber numberWithInt:p]];

     while ([powers count] > POWER_ARRAY_SIZE){
        [powers removeObjectAtIndex:0];
     }
  }

int power[ARRAYSIZE];