Question

尝试在Fraction操作上编写简单程序。无法编译代码。在“减去”方法的界面中获得“预期标识符或'（'xcode'错误。

我对这个问题进行了研究，在我看来，这是一种通用错误。这是我的计划：

#import <Foundation/Foundation.h>
// Define the Fraction class
@interface Fraction : NSObject
{
int numerator;
int denominator;
}
@property int numerator, denominator;
-(void) print;
-(void) setTo: (int) n over: (int) d;
 -(double) convertToNum;
-(Fraction *) add: (Fraction *) f;
–(Fraction *) subtract: (Fraction *) f;
–(Fraction *) multiply: (Fraction *) f;
–(Fraction *) divide: (Fraction *) f;

-(void) reduce; 
@end

#import "Fraction.h"
@implementation Fraction
@synthesize numerator, denominator;
-(void) print
{
NSLog (@"%i/%i", numerator, denominator);
}
-(double) convertToNum
{
if (denominator != 0)
return (double) numerator / denominator;
else
    return NAN;
}
-(void) setTo: (int) n over: (int) d
{
numerator = n;
denominator = d;
}
// add a Fraction to the receiver

-(Fraction *) add: (Fraction *) f
{

Fraction *result = [[Fraction alloc] init];
result.numerator = numerator * f.denominator +
denominator * f.numerator;
result.denominator = denominator * f.denominator;
[result reduce];
return result;
}

-(Fraction *) subtract: (Fraction *) f
{
Fraction *result = [[Fraction alloc] init];
result.numerator = numerator * f.denominator -
denominator * f.numerator;
result.denominator = denominator * f.denominator;
[result reduce];
return result;
}

-(Fraction *) multiply: (Fraction *) f
{
Fraction *result= [[Fraction alloc] init];

result.numerator = numerator * f.numerator;
result.denominator = denominator * f.denominator;
[result reduce];
return result;

}


-(Fraction *) divide: (Fraction *) f;
{
Fraction *result = [[Fraction alloc] init];
result.numerator= numerator * f.denominator;
result.denominator = denominator * f.numerator;
[result reduce];
return result;
}

-(void) reduce
{
int u = numerator;
int v = denominator;
int temp;
while (v != 0) {
temp = u % v;
u = v;
v = temp;
}
numerator /= u;
denominator /= u;
}
@end
#import "Fraction.h"

int main (int argc, char *argv[])
{
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];


Fraction *myFraction1 = [[Fraction alloc] init];
Fraction *myFraction2 = [[Fraction alloc] init];


[myFraction2 setTo:200 over:300];

[myFraction1 setTo: 100 over: 300];




[myFraction2 subtract: myFraction1];


NSLog (@"The value of myFraction2 is:");

[myFraction2 print];

[myFraction2 release];
[myFraction1 release];

[pool drain];
return 0;
}

Answer 1

在main：

中删除此行末尾的逗号

Fraction *myFraction2 = [[Fraction alloc] init], ;

Answer 2

假设这是一个文字复制和粘贴，你使用了错误的破折号。最后在英国和美国的键盘上，你想要的是在'0'键的右侧。您似乎正在使用en-dash。如果您仔细查看上面的商家信息，特别是顶部列表中的add:与subtract:，您会看到您的角色稍微宽一点。

尝试复制并粘贴此内容：

-(Fraction *) subtract: (Fraction *) f;

在您现有的定义中看到差异。

预期的标识符或'（'

2 个答案: