如何优雅的实现一个C++分数类(Rational) ?

时间：2015-08-09 12:40:36 阅读：343 评论：0 收藏：0 [点我收藏+]

标签：c++ rational

什么样的Rational类实现算是优雅？

在我看来它应该符合以下几个特点

1.符合面向对象的封装特性，数据隐藏（因为只有一个类，没有考虑封装和多态）。

2.声明与实现相分离，接口清晰，自然，既有足够的基本功能又不冗余。

3.代码简洁清晰

4.最好不加注释就能看懂，变量名，方法名能够见名知义

5.do not repeat yourself，不要做重复的工作

6.出错时抛出异常，中止程序，而不是将错误掩盖在内部实现之中，埋下隐患。

下面的这个Rational实现我认为是比较优雅的，它符合上面的5个特点

1.public ，private展示了其数据隐藏特点，分子，分母类的使用者不可访问

2.提供了加减乘除相反数倒数相等的基本操作，而且重载了+，-，*，/操作符，使用时可以更加清晰自然

3.每个方法的实现本身就不复杂，gcd函数的实现更是非常简洁

4.方法名，分子分母基本能够见名知义

5.减法用加上相反数来实现，除法用乘以倒数来实现，能够体现这一点

6.分母为零时，分子为零求倒数时抛出异常

rational.h

#ifndef Rational_
#define Rational_
#include "myException.h"
#include<iostream>
using namespace std;

class Rational{
public:
    Rational(int x, int y);//传入分子分母构造分数
    Rational(string s);//从字符串构造分数
    Rational nega();//相反数
    Rational reci();//倒数
    bool isEqual(Rational that);
    Rational add(Rational that);//加法
    Rational sub(Rational that);//减法
    Rational mul(Rational that);//乘法
    Rational div(Rational that);//除法
    void Output(ostream &out)const;//输出方法
    int getNumer(){return numer;}
    int getDenom(){return denom;}
private:
    int numer;//分子
    int denom;//分母
    int gcd(int a, int b) const { return (b==0) ? a : gcd(b, a % b); }//最大公约数
};
#endif // Rational_define

Rational.cpp

#include "rational.h"
#include "myException.h"
#include<cstdlib>

using namespace std;

Rational::Rational(int x, int y){//传入分子分母构造分数
    if(y==0) throw new illegalDenominatorValue();
    numer = x;
    denom = y;
}
//从字符串构造分数
Rational::Rational(string s){
    int pos = s.find('/',0);
    if(pos <= 0 || pos >= s.length()-1) throw new illegalInputExpression();
    numer = atoi( s.substr(0,pos).c_str() );
    denom = atoi( s.substr(pos+1,s.length()-pos-1).c_str() );
    if(denom == 0 ) throw new illegalDenominatorValue();
}
//相反数
Rational Rational::nega(){
    return Rational(-numer, denom);
}
//倒数
Rational Rational::reci(){
    if(numer == 0) throw new NoReciprocal();
    return Rational(denom,numer);
}
//相等
 bool Rational::isEqual(Rational that){
    return numer * that.denom == denom * that.numer;
 }
//加法
Rational Rational::add(Rational that){
    return Rational(numer * that.denom + denom * that.numer,denom * that.denom);
}
//减法
Rational Rational::sub(Rational that){
    return add(that.nega());
}
//乘法
Rational Rational::mul(Rational that){
    return Rational(numer  *  that.numer, denom * that.denom);
}
//除法
Rational Rational::div(Rational that){
    return mul(that.reci());
}
//输出
 void Rational::Output(ostream &out)const{
        int c = gcd(numer,denom);
       // int c = 1;
        out<<numer/c<<"/"<<denom/c;
 }
 //输出操作符重载
ostream& operator<<(ostream& out, const Rational& r){
    r.Output(out);
    return out;
}
//操作符重载
Rational operator +(Rational a, Rational b){
    return a.add(b);
}
Rational operator -(Rational a, Rational b){
    return a.sub(b);
}
Rational operator *(Rational a, Rational b){
    return a.mul(b);
}
Rational operator /(Rational a, Rational b){
    return a.div(b);
}

myException.h

// exception classes for various error types

#ifndef myExceptions_
#define myExceptions_
#include <string>
#include<iostream>
using namespace std;

// illegal Denominator value
class illegalDenominatorValue
{
   public:
      illegalDenominatorValue(string theMessage = "Denominator must be nonezero!"){
          message = theMessage;
      }
      void outputMessage() {cout << message << endl;}
   private:
      string message;
};

// illegal input Expression
class illegalInputExpression
{
   public:
      illegalInputExpression(string theMessage = "Illegal  input Expression"){
          message = theMessage;
      }
      void outputMessage() {cout << message << endl;}
   private:
      string message;
};
//倒数
class NoReciprocal
{
   public:
      NoReciprocal(string theMessage = "No Reciprocal with numerator=0"){
          message = theMessage;
      }
      void outputMessage() {cout << message << endl;}
   private:
      string message;
};
#endif

test.cpp

#include "rational.h"
#include "Rational.cpp"
using namespace std;
int main(){
    Rational a(1,2);
    Rational b("1/4");
    //Rational c("1/0");
    //Rational c("1/");
    cout<<"a =  \t"<<   a       <<endl;
    cout<<"b =  \t"<<   b       <<endl;
    cout<<"-a = \t"<<   a.nega()<<endl;
    cout<<"1/b =\t"<<   b.reci()<<endl;

    cout<<"a.add(b) =\t"<<   a.add(b)<<endl;
    cout<<"a.sub(b) =\t"<<   a.sub(b)<<endl;
    cout<<"a.mul(b) =\t"<<   a.mul(b)<<endl;
    cout<<"a.div(b) =\t"<<   a.div(b)<<endl;

    cout<<"a+b =\t"<<   a+b<<endl;
    cout<<"a-b =\t"<<   a-b<<endl;
    cout<<"a*b =\t"<<   a*b<<endl;
    cout<<"a/c =\t"<<   a/b<<endl;

    return 0;
}

作为一个例子，我们来看如何使用这个类解决“求解形如a/b x+ c/d = e/f的一元一次分式方程”的问题