xcode calculator app method - xcode

Question

I'm doing a calculator app base on a online tutorial, itunes.apple. com/itunes-u/ipad-iphone-application- development/ id473757255 (tut 2)
I followed every step closely and all was fine, until the finishing step of a method call performOperation. When I build and run, the numbers and enter function work fine. Only the operation method is not working. So I presume that the main trouble is with the operation method.
BrainCalculator.h
#interface CalculatorBrain : NSObject
-(void) pushOperand: (double)operand;
-(double) performOperation: (NSString*) operation;
#end
BrainCalculator.m
#import "CalculatorBrain.h"
#interface CalculatorBrain()
#property (nonatomic, strong) NSMutableArray* _operandStack;
#end
#implementation CalculatorBrain
#synthesize _operandStack;
-(NSMutableArray *)operandStack
{
if (!_operandStack){
_operandStack= [[NSMutableArray alloc ]init];
}
return _operandStack;
}
-(void)pushOperand:(double)operand{
NSNumber *operandObject = [NSNumber numberWithDouble:operand];
[self.operandStack addObject:operandObject];
}
-(double)popOperand{
NSNumber *operandObject= [self.operandStack lastObject];
if (operandObject) [self.operandStack removeLastObject];
return [operandObject doubleValue];
}
-(double)performOperation:(NSString *)operation
{
double result = 0;
if ([operation isEqualToString:#"+"]){
result=[self popOperand] + [self popOperand];
}else if ([#"*" isEqualToString:operation]){
result = [self popOperand] * [self popOperand];
}else if ([operation isEqualToString:#"-"]){
double subtrahend = [self popOperand];
result = [self popOperand] - subtrahend;
}else if( [operation isEqualToString:#"/"]){
double divisor = [self popOperand];
if (divisor) result = [self popOperand] / divisor;
}
[self pushOperand:result];
return result;
}
#end
Initially, it seem to me that the performOperation method was pretty fishy, so I tried fiddling the
}else if ([#"*" isEqualToString:operation]){
to
}else if ([operation isEqualToString:#"*"]){
hoping it would work, but sadly it didn't.
Just for additional information
viewcontroller.m
#import "CalculatorViewController.h"
#import "CalculatorBrain.h"
#interface CalculatorViewController ()
#property (nonatomic) BOOL userIsInTheMiddleOfEnteringANumber;
#property (nonatomic, strong) CalculatorBrain *brain;
#end
#implementation CalculatorViewController
#synthesize display;
#synthesize userIsInTheMiddleOfEnteringANumber;
#synthesize brain= _brain;
-(CalculatorBrain*)brain
{
if(!_brain)_brain = [[CalculatorBrain alloc]init];
return _brain;
}
- (IBAction)digitPressed:(UIButton *)sender {
NSString * digit= [ sender currentTitle];
if (userIsInTheMiddleOfEnteringANumber){
self.display.text = [self.display.text stringByAppendingString:digit];
}
else{
self.display.text=digit;
self.userIsInTheMiddleOfEnteringANumber = YES;
}
}
- (IBAction)enterPressed {
[self.brain pushOperand:[self.display.text doubleValue]];
self.userIsInTheMiddleOfEnteringANumber = NO;
}
- (IBAction)operationPressed:(UIButton *)sender {
if (self.userIsInTheMiddleOfEnteringANumber){
[self enterPressed];
}
NSString *operation = [sender currentTitle];
double result = [self.brain performOperation:operation];
self.display.text = [NSString stringWithFormat:#"%g", result];
}
#end
help will be greatly appreciated as I'm practising xcode to prepare myself for my final year major project.