c++ - 如何修复分数类的重载 + 运算符的输出？

Question

我对我的 fractionType 类有疑问。我正在为赋值编码，赋值要求我重载基本算术运算符(+、-、/、*)、逻辑运算符(==、<、>、=<、=>)和系统运算符(<< , >>)到目前为止，我有系统运算符在工作，以及乘法和除法运算符。当我测试 + 和 - 运算符时，我的问题出现了。我的输入被硬编码为 2/4 和 1/8，但我的输出是 3/8。这是不对的。

我的代码来自 fractionType.cpp

#include <iostream>
#include "fractionType.h"

fractionType::fractionType(){
}
fractionType::fractionType(int a, int b) {
  numerator = a;
  denominator = b;
}
fractionType fractionType::operator+(fractionType fraction) {
  fractionType anotherFraction;
  if (denominator = fraction.denominator) {

      anotherFraction.numerator = numerator + fraction.numerator;

      anotherFraction.denominator = denominator;
  }
if (denominator != fraction.denominator) {
    anotherFraction.numerator = ((numerator) * (fraction.denominator)) +         ((fraction.numerator) * (denominator));

    anotherFraction.denominator = denominator * fraction.denominator;
}
return anotherFraction;
}
fractionType fractionType::operator-(fractionType fraction) {

fractionType anotherFraction;

if (denominator = fraction.denominator) {

    anotherFraction.numerator = numerator - fraction.numerator;

    anotherFraction.denominator = denominator;
}
else {
    anotherFraction.numerator = (numerator * fraction.denominator) - (fraction.numerator * fraction.denominator);

    anotherFraction.denominator = denominator * fraction.denominator;
}

return anotherFraction;


}

我的代码来自 fractionType.h

#include <iostream>

class fractionType {
public: 
  fractionType(int a, int b);
  fractionType();
  fractionType operator*(fractionType fraction);
  fractionType operator/(fractionType fraction);
  fractionType operator+(fractionType fraction);
  fractionType operator-(fractionType fraction);
  friend std::ostream& operator<<(std::ostream& out, const fractionType &fraction) {
    out << fraction.numerator << '/' << fraction.denominator;
    return out;
}
friend std::istream& operator>> (std::istream& in, fractionType &fraction) {
    char c;
    in >> fraction.numerator >> c >> fraction.denominator;
    return in;
}
private:
int numerator, denominator;
};
#endif FRACTIONTYPE_H

和我的 source.cpp

#include <iostream>
#include "fractionType.h"

int main() {
  fractionType aFraction(2, 4);
  fractionType bFraction(1, 8);
  fractionType cFraction;
  cFraction = aFraction + bFraction;
  std::cout << cFraction << std::endl;
  system("PAUSE");
}

我删除了我的 operator* 和 operator/，因为它们可以正常工作。我不知道我做错了什么，在我发布这个问题之前我已经一遍又一遍地复习数学。是因为我没有使用指针吗？常量？或者它有什么不同？在此先感谢您的帮助!

Answer 1

这一行是错误的:

if (denominator = fraction.denominator) {

必须是

if (denominator == fraction.denominator) {

如果启用警告，clang 和 gcc 会告诉您，例如:

main.cpp:32:19: warning: using the result of an assignment as a condition without parentheses [-Wparentheses]

  if (denominator = fraction.denominator) {

      ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

live example

如果您更正了上述错误，您的代码就可以工作了:

输出

20/32

live example