fraction.cpp

BigC++的源码

#include "fraction.h"
#include <cassert>
#include <stdexcept>

int Fraction::gcd(int n, int m)
{
   // Euclid's Greatest Common Divisor algorithm.
   assert((n > 0) && (m > 0));
   while (n != m)
   {
      if (n < m)
      m = m - n;
      else
      n = n - m;
   }
   return n;
}

Fraction::Fraction(int t, int b) : top(t), bottom(b)
{
    normalize();
}

Fraction::Fraction() : top(0), bottom(1) { }

Fraction::Fraction(int t) : top(t), bottom(1) { }

int Fraction::numerator() const
{
    return top;
}

int Fraction::denominator() const
{
    return bottom;
}

void Fraction::normalize()
{
   // Normalize fraction by
   // (a) moving sign to numerator
   // (b) ensuring numerator and denominator have no common divisors
   int sign = 1;
   if (top < 0) 
   {
      sign = -1;
      top = - top;
   }
   if (bottom < 0) 
   {
      sign = - sign;
      bottom = - bottom;
   }
   assert(bottom != 0);
   int d = 1;
   if (top > 0) d = gcd(top, bottom);
   top = sign * (top / d);
   bottom = bottom / d;
}

Fraction operator+(const Fraction& left, const Fraction& right)
{
   Fraction result(left.numerator() * right.denominator()
      + right.numerator() * left.denominator(),
      left.denominator() * right.denominator());
   return result;
}

Fraction operator-(const Fraction& left, const Fraction& right)
{
   Fraction result(left.numerator() * right.denominator()
      - right.numerator() * left.denominator(),
      left.denominator() * right.denominator());
   return result;
}

Fraction operator*(const Fraction& left, const Fraction& right)
{
   Fraction result(left.numerator() * right.numerator(),
      left.denominator() * right.denominator());
   return result;
}

Fraction operator/(const Fraction& left, const Fraction& right)
{
   Fraction result(left.numerator() * right.denominator(),
      left.denominator() * right.numerator());
   return result;
}

Fraction operator-(const Fraction& value)
{
   Fraction result(-value.numerator(), value.denominator());
   return result;
}

int Fraction::compare(const Fraction& right) const
{
   return numerator() * right.denominator()  
      - denominator() * right.numerator();
   // Return the numerator of the difference
}

bool operator<(const Fraction& left, const Fraction& right)
{
   return left.compare(right) < 0;
}

bool operator<=(const Fraction& left, const Fraction& right)
{
   return left.compare(right) <= 0;
}

bool operator==(const Fraction& left, const Fraction& right)
{
   return left.compare(right) == 0;
}

bool operator!=(const Fraction& left, const Fraction& right)
{
   return left.compare(right) != 0;
}

bool operator>=(const Fraction& left, const Fraction& right)
{
   return left.compare(right) >= 0;
}

bool operator>(const Fraction& left, const Fraction& right)
{
   return left.compare(right) > 0;
}

ostream& operator<<(ostream& out, const Fraction& value)
{
   out << value.numerator() << "/" << value.denominator();
   return out;
}

istream& operator>>(istream& in, Fraction& r)
{
   int t, b;
   // Read the top
   in >> t;
   // If there is a slash, read the next number
   char c;
   in >> c;
   if (c == '/')
      in >> b;
   else
   {
      in.putback(c);
      b = 1;
   }
   r = Fraction(t, b);
   return in;
}

Fraction::operator double() const
{
      // Convert numerator to double, then divide
   return static_cast<double>(top) / bottom;
}

Fraction& Fraction::operator++()
{
   top += bottom;
   return *this;
}

Fraction Fraction::operator++(int unused)
{
   Fraction clone(top, bottom);
   top += bottom;
   return clone;
}

Fraction& Fraction::operator+=(const Fraction& right)
{
   top = top * right.denominator() + bottom * right.numerator();
   bottom *= right.denominator();
   normalize();
   return *this;
}