c++ - 为什么我的成员函数不起作用？

Question

我正在为计算机程序类编写计算机程序，但是由于某种原因，由于涉及成员函数的错误，我无法运行程序。我不断收到错误消息

“错误错误C3490:'den'无法修改，因为正在通过const对象访问它”

收到此消息我做错了什么，如何纠正它？

这是我的代码:

 // implement all class member functions here, gcd function is given

 int Fraction::gcd()
 {
if(num == 0) return 1;

        int a = max(abs(num), abs(den));
        int b = min(abs(num), abs(den));

while(b != 0)
{
    int result = a%b;
    a = b;
    b = result;
}

return a;
}
 void Fraction::input(istream& in)
{
char op;
in >> num;
in >> op;
in >> den;
if(den == 0)
{
    cout << "Wrong input. Exit the program" << endl;
    exit(1);
}
 if(den < 0)
{
 num *= -1;
 den *= -1;}
}
 void Fraction::output(ostream& out)
 {
  if(den == 0)
 out << "0";
  else
 out << num << " / " << den;
}

 Fraction::Fraction(int numerator, int denominator)
 {
   assert(denominator !=0);
   num = numerator;
   den = denominator;
if(den < 0)
{
   num *=-1;
   den *= -1;
}
}
 bool Fraction::less(const Fraction& other) const
 {
Fraction temp(other.num , other.den);
int num_1(num);
if(den != temp.den)
{
    num_1 *= temp.den;
    temp.num *= num;
}
if(num_1 < temp.num)
  {return true;}
else
  {return false;}
 }
  Fraction Fraction::reciprocal() const
 {
  Fraction tempa(num, den);
  int temp(tempa.num);
  tempa.num = tempa.den;
  tempa.den = temp;
  num = den;
if(den < 0)
{
  num *= -1;
  den *= -1;
} 
return tempa;
  }
 Fraction Fraction::neg() const
  {
  num*=-1;
  return;  
  }  
  Fraction::Fraction(int numerator)
  {
   num = numerator;
   den = 1;
  }
  Fraction::Fraction()
  {
   num = 0;
   den = 1;
}
Fraction Fraction::add(const Fraction& other) const 
{
int num_1 = num *other.den;
int num_2 = den*other.den;
int denom = den*other.den;
 Fraction result((num_1+num_2), denom);
   result.reduce();
   return result;
 }
 Fraction Fraction::div(const Fraction& other) const
 {
   Fraction temp(num, den);
   other = other.reciprocal();
   Fraction result(temp.mul(other));
   return result;
}
Fraction Fraction::sub(const Fraction& other) const
{
  int num_1 = num *other.den;
  int num_2 = den*other.den;
  int denom = den*other.den;
  Fraction result((num_1-num_2), denom);
  result.reduce();
  return result;
}
Fraction Fraction::mul(const Fraction& other) const
{
  int num_0 = num*other.num;
  int denom = den*other.den;
  Fraction result(num_0, denom);
  result.reduce();
  return result;
}
 void Fraction::reduce()
 {
  int r = gcd();
  num /= r;
  den /= r;
  if(num == 0)
    den = 1;

}
bool Fraction::less_or_equal(const Fraction& other) const
{

}
bool Fraction::greater_or_equal(const Fraction& other) const
{

}
bool Fraction::equal(const Fraction& other) const
{

}
bool Fraction::not_equal(const Fraction& other) const
{

}
bool Fraction::greater(const Fraction& other) 

Answer 1

您正在尝试在const方法中修改名为“den”的成员，并且无法在const内部进行任何修改，仅访问数据即可。您将需要修改函数以删除const或在不使用const的情况下复制它。

您的代码很难阅读，但这似乎发生在您的“reciprocal()”方法中。