Creating length objects - C++ Class

C++ examples for Class:Inheritance

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Description

Creating length objects

Demo Code

#include <iostream>
#include <iomanip>
#include <memory>
#include <string>
#include <typeinfo>
#include <vector>
using std::string;
    /*from  w  ww .  j  a  va  2  s  .  c om*/
class MyLength
{
protected:
  long mm{};
  static double mmPerInch;
  static double mmPerMeter;
  static double inchesPerYard;
  static double yardsPerPerch;
    
public:
  MyLength() = default;                                                           // Default constructor
  MyLength(long n) : mm(n) {}                                                      // Constructor from millimeters
  virtual double length() const { return mm; };                                     // Return the length
};
    
class Inches : public MyLength
{
protected:
  double inches{};
    
public:
  Inches() = default;
  Inches(double ins) :MyLength{ static_cast<long>(0.5 + mmPerInch*ins) }, inches{ ins } {}
  double length() const override { return inches; }                                 // Return the length
};
    
class Meters : public MyLength
{
protected:
  double meters{};
    
public:
  Meters() = default;
  Meters(double m) :MyLength{ static_cast<long>(0.5 + mmPerMeter*m) }, meters{ m } {}
  double length() const override { return meters; }                                 // Return the length
};
    
class Yards : public MyLength
{
protected:
  double yards{};
    
public:
  Yards() = default;
  Yards(double yds) :MyLength{ static_cast<long>(0.5 + inchesPerYard*mmPerInch*yds) }, yards{ yds } {}
  double length() const override { return yards; }                                  // Return the length
};
    
class Perches : public MyLength
{
protected:
  double perches{};
    
public:
  Perches() :MyLength() {}
  Perches(double pch) :MyLength{ static_cast<long>(0.5 + yardsPerPerch*inchesPerYard*mmPerInch*pch) }, perches{ pch } {}
  double length() const override { return perches; }                                // Return the length
};
    
// Initialize static data members
double MyLength::mmPerInch{ 25.4 };
double MyLength::mmPerMeter{ 1000.0 };
double MyLength::inchesPerYard{ 36.0 };
double MyLength::yardsPerPerch{ 5.5 };
    
// Read a length from the keyboard
std::shared_ptr<MyLength> readLength()
{
  double value{};                                 // Stores the length value
  string units;                                    // Stores the units
    
  for (;;)
  {
    std::cout << "\nEnter a length: ";
    std::cin >> std::skipws >> value;              // Skip whitespace and read the value
    if (!value) return nullptr;
    
    getline(std::cin, units);                      // Rest of line is units
    unsigned int index{ units.find_first_not_of(" ") };   // Find first non-blank in units
    
                           // Return the object type corresponding to the units
    switch (toupper(units[index]))
    {
    case 'M':
      return std::make_shared<Meters>(value);
    case 'I':
      return std::make_shared<Inches>(value);
    case 'Y':
      return std::make_shared<Yards>(value);;
    case 'P':
      return std::make_shared<Perches>(value);
    default:
      std::cout << "\nInvalid units. Re-enter length: ";
      break;
    }
  }
}
    
int main()
{
  std::vector<std::shared_ptr<MyLength> > pLengths;
  std::cout << "\nYou can enter lengths in inches, meters, yards, or perches."
    << "\nThe first character following the number specifies the units."
    << "\nThis can be i, m, y, or p, for inches, meters, yards, or perches."
    << "\ne.g. '22 ins' is 22 inches, '3.5 p' or '3.5perches' is 3.5 perches, '1y' is 1 yard."
    << std::endl
    << "\nPlease enter a length followed by the units or 0 to end:";
    
  while (true)
  {
    auto p = readLength();
    if (!p)break;
    
    pLengths.push_back(p);
    
  }
    
  // Output the lengths - we must figure out what type they are to display the units
  for (auto p : pLengths)
  {
    string units(" invalid type");
    if (typeid(*p) == typeid(Inches))
      units = " inches";
    else if (typeid(*p) == typeid(Meters))
      units = " meters";
    else if (typeid(*p) == typeid(Yards))
      units = " yards";
    else if (typeid(*p) == typeid(Perches))
      units = " perches";
    std::cout << "\nLength is " << std::fixed << std::setprecision(2) << p->length() << units
      << " which is " << static_cast<long>(p->MyLength::length()) << " millimeters." << std::endl;
  }
}

Result


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