否定分數，但不能修改原始分數

Question

我已經編寫了以下用於修改分數對象的類。

#include "Fraction.h" 
#include "GCD.h" 
#include <iostream> 
using std::cout; 

//Implementation of the timesEq() member function 
//Performs similar operation as the *= operator on the built-in types 
const Fraction & Fraction::timesEq(const Fraction & op) 
{ 
    numerator *= op.numerator; 
    denominator *= op.denominator; 

    simplify(); // will make sure that denominator is positive and 
       // will invoke gcd() function to reduce fraction 
       // as much as possible 

    return (*this); // returns the object which invoked the method 
} 

const Fraction & Fraction::plusEq (const Fraction & op) 
{ 
    numerator *= op.denominator; 
    numerator += op.numerator * denominator; 
    denominator *= op.denominator; 

    simplify(); // will make sure that denominator is positive and 
       // will invoke gcd() function to reduce fraction 
       // as much as possible 

    return (*this); // returns the object which invoked the method 
} 

const Fraction & Fraction::minusEq (const Fraction & op) 
{ 
    numerator *= op.denominator; 
    denominator = denominator * op.denominator; 
    numerator -= op.numerator; 

    simplify(); // will make sure that denominator is positive and 
       // will invoke gcd() function to reduce fraction 
       // as much as possible 

    return (*this); // returns the object which invoked the method 
} 

const Fraction & Fraction::divideEq (const Fraction & op) 
{ 
    numerator *= op.denominator; 
    denominator *= op.numerator; 

    simplify(); // will make sure that denominator is positive and 
       // will invoke gcd() function to reduce fraction 
       // as much as possible 

    return (*this); // returns the object which invoked the method 
} 

Fraction Fraction::negate(void) const 
{ 
    return (*this * -1); 
} 

void Fraction::display(void)const { 
    cout << numerator << "/" << denominator; 
} 

void Fraction::simplify(void) 
{ 
    gcd = gcd(numerator, denominator); 
    numerator /= gcd; 
    denominator /= gcd; 
} 

但我在negate函數有問題。 我正在使用像這樣的函數：B = A.negate()，因此，我無法修改原始的A對象，但需要將否定對象指定給B。

現在我有實現是給了一個錯誤：
Error: no operator "*" matches these operands
operand types are: const Fraction * int

我不知道我做錯了。什麼需要改變？

Answer 1

假設你有一個構造函數，需要兩個int S作爲參數（如果你不這樣做，你應該，而不是隻爲我的答案的緣故），這樣做：

return Fraction(-numerator, denominator);