C++计算倒数的代码

C++计算倒数的代码

#include <iostream>  
  
using namespace std;  
  
class Var;  
  
class Base {  
public:  
  virtual ~Base() {};  
  virtual const Base *clone() = 0;  
  virtual const Base *d(const string &v) const = 0;  
  virtual ostream &print(ostream &o) const = 0;  
};  
  
ostream &operator<<(ostream &o, const Base &e) { e.print(o); return o; }  
  
class Int : public Base {  
  const int n;  
public:  
  Int(int m) : n(m) {}  
  ~Int() {}  
  const Base *clone() { return new Int(n); }  
  const Base *d(const string &v) const { return new Int(0); }  
  ostream &print(ostream &o) const { return o << n; }  
};  
  
class Var : public Base {  
  const string var;  
public:  
  Var(string v) : var(v) {}  
  ~Var() {}  
  const Base *clone() { return new Var(var); }  
  const Base *d(const string &v) const { return new Int(var == v ? 1 : 0); }  
  ostream &print(ostream &o) const { return o << var; }  
};  
  
class Plus : public Base {  
  const Base *e1, *e2;  
public:  
  Plus(const Base *a, const Base *b) : e1(a), e2(b) {}  
  ~Plus() { delete e1; delete e2; }  
  const Base *clone() { return new Plus(e1, e2); }  
  const Base *d(const string &v) const { return new Plus(e1->d(v), e2->d(v)); }  
  ostream &print(ostream &o) const  
  { return o << "(" << *e1 << " + " << *e2 << ")"; }  
};  
  
class Times : public Base {  
  const Base *e1, *e2;  
public:  
  Times(const Base *a, const Base *b) : e1(a), e2(b) {}  
  ~Times() { delete e1; delete e2; }  
  const Base *clone() { return new Times(e1, e2); }  
  const Base *d(const string &v) const  
  { return new Plus(new Times(e1, e2->d(v)), new Times(e1->d(v), e2)); }  
  ostream &print(ostream &o) const { return o << "(" << *e1 << " * " << *e2 << ")"; }  
};  
  
class Expr {  
public:  
  Base *e;  
  Expr(Base *a) : e(a) {}  
};  
  
const Expr operator+(const Expr e1, const Expr e2)  
{ return Expr(new Plus(e1.e->clone(), e2.e->clone())); }  
const Expr operator*(const Expr e1, const Expr e2)  
{ return Expr(new Times(e1.e->clone(), e2.e->clone())); }  
  
ostream &operator<<(ostream &o, const Expr e) { return o << e.e; }  
  
int main() {  
  Var vx("x"), va("a"), vb("b"), vc("c");  
  Expr x(&vx), a(&va), b(&vb), c(&vc);  
  Expr e = a*x*x + b*x + c;  
  cout << "d(" << *(e.e) << ", x) = " << *(e.e->d("x")) << endl;  
  return 0;  
}