iOS RPNCalculatorStanfordVidOne无法弄清楚为什么除了一行之外的所有线路都在工作

Question

我是iOS的全新成员。我在网上看斯坦福大学的视频学习iOS。我花了几个小时慢慢地仔细浏览第二个视频，确保我没有在一行代码上犯错误。一切都很完美，直到——你不知道吗——编码的最后一分钟。

我和妻子花了很多时间试图弄清楚，但我的代码与教授的代码完全匹配。请帮帮我。我喜欢通过这些视频学习，但在我有了这个功能并花时间复习之前，我无法继续前进。

#import "CalculatorViewController.h"
#import "CalculatorBrain.h"
@interface CalculatorViewController()
@property (nonatomic) BOOL userIsInTheMiddleOfEnteringANumber;
@property (nonatomic, strong) CalculatorBrain *brain;
@end 
@implementation CalculatorViewController
@synthesize display  = _display;
@synthesize userIsInTheMiddleOfEnteringANumber = 
_userIsInTheMiddleOfEnteringANumber;
@synthesize brain = _brain;
- (CalculatorBrain *)brain
{
    if (!_brain) _brain = [[CalculatorBrain alloc] init];
    return _brain;
}
- (IBAction)digitPressed:(UIButton *)sender 
{
    NSString *digit = sender.currentTitle;
        if (self.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:(id)sender 
{
    if (self.userIsInTheMiddleOfEnteringANumber) [self enterPressed];
    double result = [self.brain performOperation:sender.currentTitle];  // <- HERE IS THE       LINE IN QUESTION
    NSString *resultString = [NSString stringWithFormat:@"%g", result];
    self.display.text = resultString;
}
@end

---

CalculatorBrain.m

#import "CalculatorBrain.h"
@interface CalculatorBrain()
@property (nonatomic, strong) NSMutableArray *operandStack;
@end
@implementation CalculatorBrain
@synthesize operandStack = _operandStack;
- (NSMutableArray *) operandStack
{
    if (_operandStack == nil) _operandStack = [[NSMutableArray alloc] init];
    return _operandStack;
}
- (void)pushOperand:(double)operand
{
    [self.operandStack addObject:[NSNumber numberWithDouble:operand]];
}
- (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];
    }
    [self pushOperand:result];
    return result;
}
@end

Answer 1

我认为问题在于if语句没有正确关闭。

- (IBAction)operationPressed:(id)sender 
{
    if (self.userIsInTheMiddleOfEnteringANumber){ [self enterPressed];
    double result = [self.brain performOperation:sender.currentTitle];  
    NSString *resultString = [NSString stringWithFormat:@"%g", result];
    self.display.text = resultString;
}
}

或

- (IBAction)operationPressed:(id)sender 
    {
        if (self.userIsInTheMiddleOfEnteringANumber)
{
 [self enterPressed];
}
        double result = [self.brain performOperation:sender.currentTitle]; 
        NSString *resultString = [NSString stringWithFormat:@"%g", result];
        self.display.text = resultString;
    }

建议查看教程的pdf文件以获得更具体的代码源。希望有帮助。