recycle.cpp

C语言数值算法程序大全（第二版）,课本文件

//: C08:Recycle.cpp
// From "Thinking in C++, 2nd Edition, Volume 2"
// by Bruce Eckel & Chuck Allison, (c) 2003 MindView, Inc.
// Available at www.BruceEckel.com.
// A Trash Recycler
#include <cstdlib>
#include <ctime>
#include <iostream>
#include <typeinfo>
#include <vector>
#include "../purge.h"
using namespace std;

class Trash {
  float _weight;
public:
  Trash(float wt) : _weight(wt) {}
  virtual float value() const = 0;
  float weight() const { return _weight; }
  virtual ~Trash() { cout << "~Trash()\n"; }
};

class Aluminum : public Trash {
  static float val;
public:
  Aluminum(float wt) : Trash(wt) {}
  float value() const { return val; }
  static void value(float newval) {
    val = newval;
  }
};
float Aluminum::val = 1.67;

class Paper : public Trash {
  static float val;
public:
  Paper(float wt) : Trash(wt) {}
  float value() const { return val; }
  static void value(float newval) {
    val = newval;
  }
};
float Paper::val = 0.10;

class Glass : public Trash {
  static float val;
public:
  Glass(float wt) : Trash(wt) {}
  float value() const { return val; }
  static void value(float newval) {
    val = newval;
  }
};
float Glass::val = 0.23;

// Sums up the value of the Trash in a bin:
template<class Container> void
sumValue(Container& bin, ostream& os) {
  typename Container::iterator tally = 
    bin.begin();
  float val = 0;
  while(tally != bin.end()) {
    val += (*tally)->weight() * (*tally)->value();
    os << "weight of "
        << typeid(**tally).name()
        << " = " << (*tally)->weight() << endl;
    tally++;
  }
  os << "Total value = " << val << endl;
}

int main() {
  srand(time(0)); // Seed random number generator
  vector<Trash*> bin;
  // Fill up the Trash bin:
  for(int i = 0; i < 30; i++)
    switch(rand() % 3) {
      case 0 :
        bin.push_back(new Aluminum((rand() % 1000)/10.0));
        break;
      case 1 :
        bin.push_back(new Paper((rand() % 1000)/10.0));
        break;
      case 2 :
        bin.push_back(new Glass((rand() % 1000)/10.0));
        break;
    }
  // Note: bins hold exact type of object, not base type:
  vector<Glass*> glassBin;
  vector<Paper*> paperBin;
  vector<Aluminum*> alumBin;
  vector<Trash*>::iterator sorter = bin.begin();
  // Sort the Trash:
  while(sorter != bin.end()) {
    Aluminum* ap =
      dynamic_cast<Aluminum*>(*sorter);
    Paper* pp =
      dynamic_cast<Paper*>(*sorter);
    Glass* gp =
      dynamic_cast<Glass*>(*sorter);
    if(ap) alumBin.push_back(ap);
    else if(pp) paperBin.push_back(pp);
    else if(gp) glassBin.push_back(gp);
    sorter++;
  }
  sumValue(alumBin, cout);
  sumValue(paperBin, cout);
  sumValue(glassBin, cout);
  sumValue(bin, cout);
  purge(bin);
} ///:~