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所以我正在学习 Xcode Objective-C 课程，我们必须制作一个计算器。一切正常，除了我必须为有人试图除以零时创建例外的部分。我一辈子都无法让它工作，我一直得到的只是计算器上的 INF 消息。他们也希望它成为一种@try @catch方法，所以我的谷歌搜索让我自己问这个问题，因为我找不到答案。这是我的完整代码。

#import "Calculator.h"

@interface ViewController ()

@end

@implementation ViewController
@synthesize numerator, denominator, total, operand, theNumber, lblText;

- (void)viewDidLoad {
    [super viewDidLoad];

    [self setNumerator:0];
    [self setDenominator:0];
    [self setOperand:PLUS];
    [self setTotal:0.0];
    [self setTheNumber:@""];

    [self printNumber];
}

-(void)printNumber
{
    [lblText setText:theNumber];
}

-(float)divideOp
   {
    float result=0;
    @try {
        if (self.denominator != 0) {
            result = (self.numerator / self.denominator);
        } else {
            result = NAN;
        }
    } @catch (NSException *exception) {
        // deal with the exception
        NSLog(@"Can't divide by 0!");
    }

    return result;
}

-(IBAction)calculate:(id)sender
{
    denominator = [theNumber integerValue];

    if(operand == PLUS)
        total = numerator + denominator;
    else if(operand == MINUS)
        total = numerator - denominator;
    else if(operand == MULTIPLY)
        total = numerator * denominator;

    theNumber = [NSString stringWithFormat:@"%f",total];
    [self printNumber];

    numerator = 0;
    denominator = 0;
    total = 0.0;
}

-(void)saveNumerator
{
    numerator = [theNumber integerValue];
    theNumber = @"0";
    [self printNumber];
}

-(IBAction)clearNum:(id)sender
{
    theNumber = @"0";
    [self printNumber];

}
-(IBAction)setPlus:(id)sender
{
    [self saveNumerator];
    operand = PLUS;
}

-(IBAction)setMinus:(id)sender
{
    [self saveNumerator];
    operand = MINUS;
}

-(IBAction)setMultiply:(id)sender
{
    [self saveNumerator];
    operand = MULTIPLY;
}

-(IBAction)setDivide:(id)sender
{
    [self saveNumerator];
    operand = DIVIDE;
}

-(IBAction)press9:(id)sender
{
    theNumber = [theNumber stringByAppendingString:@"9"];
    [self printNumber];
}

-(IBAction)press8:(id)sender
{
    theNumber = [theNumber stringByAppendingString:@"8"];
    [self printNumber];
}

-(IBAction)press7:(id)sender
{
    theNumber = [theNumber stringByAppendingString:@"7"];
    [self printNumber];
}

-(IBAction)press6:(id)sender
{
    theNumber = [theNumber stringByAppendingString:@"6"];
    [self printNumber];
}

-(IBAction)press5:(id)sender
{
    theNumber = [theNumber stringByAppendingString:@"5"];
    [self printNumber];
}

-(IBAction)press4:(id)sender
{
    theNumber = [theNumber stringByAppendingString:@"4"];
    [self printNumber];
}

-(IBAction)press3:(id)sender
{
    theNumber = [theNumber stringByAppendingString:@"3"];
    [self printNumber];
}

-(IBAction)press2:(id)sender
{
    theNumber = [theNumber stringByAppendingString:@"2"];
    [self printNumber];
}

-(IBAction)press1:(id)sender
{
    theNumber = [theNumber stringByAppendingString:@"1"];
    [self printNumber];
}

-(IBAction)press0:(id)sender
{
    theNumber = [theNumber stringByAppendingString:@"0"];
    [self printNumber];
}

@end
4

1 回答 1

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而不是设置：

result = NAN;

当你除以零时，你应该

NSException *e = [NSException
    exceptionWithName:@"Divide By Zero"
    reason:@"Divide by Zero Exception"
    userInfo:nil];
@throw e;

不要在divideOp方法中捕获异常......在任何应该打印计算结果的例程中捕获它并打印出尝试了非法除以零操作。

于 2017-05-06T03:26:59.210 回答