Understanding the concept of objects & Telephone in C++ pro

Understanding the concept of objects

#include 

#include 

#include 

enum color {red, blue, white, green, yellow};

const double dummy = 0.0; 

const color dummyc = white; 

void show (color);

void point (char, double); 

void colorpoint (char, double, color);

void main () 

{

  point('O', dummy);

  point('p', dummy);

  point('x', 8.0);

  point('p', dummy);

  point('y', 7.0);

  point('p', dummy);

  point('x', 2.0);

  point('p', dummy);

  point('x', 3.0);

  point('p', dummy);

  point('o', dummy);

  point('p', dummy);

  colorpoint('o',dummy,dummyc);

  colorpoint('p',dummy,dummyc);

  colorpoint('c',dummy,blue);

  colorpoint('p',dummy,dummyc);

  colorpoint('x',2.0,dummyc);

  colorpoint('p',dummy,dummyc);

}

void point (char message, double data) 

{

  static double x_coord = 0.0;

  static double y_coord = 0.0;

  static double distance = 0.0;

  switch (message) 

 {

  case 'X': 

    x_coord = x_coord + data;

    break;

  case 'Y': 

    y_coord = y_coord + data;

    break;

  case 'O': 

    x_coord = 0.0;

    y_coord = 0.0;

    break;

 case 'P': 

 cout << "I am currently at x = " << x_coord << ", y = " << y_coord << endl;

    cout << "My distance from the origin is " << distance << endl;

    break;

  default: 

    cout << "Unknown message to point" << endl;

    exit(-1);

  }

  distance = sqrt (x_coord * x_coord + y_coord * y_coord);

  return;

}

void colorpoint (char message, double data, color color) 

{

  static color col = white;

  switch (message) 

{

  case 'x':

  case 'y': 

  case 'o':

    point(message,data);

    break;

  case 'c': 

    col = color;

    break;

  case 'p': 

    point('p',dummy);

    cout << "Also my color is ";

    show(col);

    cout << endl;

    break;

  default: 

    cout << "Unknown message to colorPoint" << endl;

    exit(-1);

  }

  return;

}

void show (Color col) 

{

  switch (col) 

{

  case red: 

    cout << "Red";

    break;

  case blue: 

    cout << "Blue";

    break;

  case white: 

    cout << "White";

    break;

  case green: 

    cout << "Green";

    break;

  case yellow:

    cout << "Yellow";

    break;

  }

}

Telephone

#include 

#include

#include 

#include 

typedef int bool;

const bool true = 1;

const bool false = 0;

void readLetter(char&);

int computecorrespondingdigit(char);

bool dooneletter(); 

void main () 

{

  bool flag = false;

  while (!flag) 

   {

    flag = dooneletter();

  }

}  

int exitLetter (char c) 

{

  return ((c == 'Q') || (c == 'Z'));

}

bool dooneletter() 

{

  char l;

  int i;

  readLetter(l);

  if (exitLetter(l)) 

  {

    cout << "Quit." << endl;

    return(true);

  }

  else 

 {

    i = computeCorrespondingDigit(l);

    cout << "The letter " << l << " corresponds to " << i 

      << " on the telephone" << endl;

    return(false);

  }

}

int computecorrespondingdigit (char l) 

{

  switch (l) 

 {

  case 'a' : 

  case 'b' :

  case 'c' : 

    return(2);

  case 'd' : 

  case 'e' :

  case 'f' : 

    return(3);

  case 'g' : 

  case 'h' :

  case 'i' : 

    return(4);

  case 'j' : 

  case 'k' :

  case 'l' : 

    return(5);

  case 'm' : 

  case 'n' :

  case 'o' : 

    return(6);

  case 'p' : 

  case 'r' :

  case 's' : 

    return(7);

  case 't' : 

  case 'u' :

  case 'v' : 

    return(8);

  case 'w' : 

  case 'x' :

  case 'y' : 

    return(9);

  }

}

void readletter(char& c) 

{

  cout << "Enter a letter: ";

  cin >> c;

  while (cin && !isalpha(c)) 

  {

    cout << "You have not entered a letter. Try again: ";

    cin >> c;

  }

  if (!cin) 

   {

    cout << "Unrecoverable error... Exiting" << endl;

    exit(-1);

  }

  c = toupper(c);

}