C++ programming language

�� C⁺⁺
�� 34
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(Arrays as Instance Data)
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1. �� (Sizing an Array). � �� 31 � �� stackcon.cpp �� st �� 20 �� :

class Stack                   // a stack holds up to 20 ints
{
   private:
      int st[20];             // integers are stored in array
      int top;                // index of last item pushed

public:
. . .

};

�� ?

1. �� 20 �� . �� , �� .

2. �� 19 (20 - 1) � �� push(), �� :

void push(int var)
{
if(top >= 19)                // if at or beyond the end of array,
    cout << "Illegal push";    // error message
else
    st(++top) = var;
}

�� , �� , �� (�� ), �� , �� .

�� (array sized with external const), �� - �� size �� array_size �� -�� stack_array_size. �� .

// size of st variable of Stack class
const int stack_array_size = 20;

�� 27 �� . �� , �� (�� ).

2. �� (Initializing Member Variables). �� -��

Stack
{
private:
    const int size = 20; // illegal initialization!!!
    int st[size];
    int top;
public:
. . .

};

� ��

Cannot initialize a class member here.

�� (initialization list), �� 32. �� , �� -�� , �� ��  �� . �� , �� .

�� , �� size � ��

Stack() : top(-1), size(20) // constructor
{ }

�� , �� ��  �� , �.�. �� , � �� ! �.�. ��

int st[size];

�� , �� size � ��

class Stack            // a stack holds up to 20 ints
{
   private:
     const int size;   // array size; mention that it is defined as constant!!!
     int st[size];     // the constructor complains "Constant expression required."!!!
     int top;          // index of last item pushed

   public:
     Stack() : top(-1), size(20) // constructor with an initialization of size!
     {   }

. . .

};

��

Constant expression required.

�� , �� (Initialization Is Not Assignment) � �� , �� size, �� size = 20;, �� -��:

class Stack                   // a stack holds up to 20 ints
{
   private:
     const int size; // array size
     int st[size];           // integers are stored in array
     int top;                // index of last item pushed

   public:
     Stack() : top(-1)       // constructor
     {
       size = 20;
     }

. . .

}

�� :

Constant member 'Stack::size' is not initialized.

Cannot modify a const object.

�� , �� (�� ), �� , �� (�.�. ��-��).

3. �� (The enum Hack). �� Hack [1], �� "�� ", (�� ), �� -�� , � �� . �� , �� (enum), �� . (�� 22).

class Stack
{
private:
    enum { size = 20 }; // established at compile time
    int st[size];        // OK
    int top;

. . .

};

�� , �� size � �� 20. �� , �� , �� . �� C++ �� ANSI/ISO �� .

4. �� (Static Constant Variables). �� , �� [1] �� . �� , �� :

class Stack
{
private:
    static const int size = 20; // static constant
    int st[size];
    int top;

. . .

}

�� size �� (�� !), �� , �� st. �� 28.

�� staticon.cpp, �� stackcon.cpp �� 31.

// staticon.cpp
// class models a stack
// uses static constant for member array size
#include <iostream.h>
#include <conio.h> // for getch()

class Stack                   // a stack holds up to 20 ints
{
   private:
      static const int size = 20; // array size
      int st[size];           // integers are stored in array
      int top;                // index of last item pushed

   public:
      Stack() : top(-1)       // constructor
      {   }

      void push(int var)      // place an item on the stack
      {
        if(top >= size - 1)                // if at or beyond the end of array,
          cout << "Illegal push";    // error message
        else
          st[++top] = var;
      }

      // remove an item from the stack
      int pop()
      {
        if (top < 0)                                 // if beyond the beginning of array,
        {
          cout << "Cannot pop: stack is emty! ";     // error message
          return 0;
        }
        else
          return st[top--];
      }
}; // class Stack

void main()
{
   Stack s1;                  // create a stack object
   s1.push(11);               // push 3 items onto stack
   s1.push(12);
   s1.push(13);

   cout << s1.pop() << endl; // pop 3 items and display them
   cout << s1.pop() << endl;
   cout << s1.pop() << endl;

getch();
} // main()

�� if(top >= size - 1), �� top = size - 1 (�� !) �� top > size - 1. �� pop(): �� return 0; � �� , �� cout �� , �� , �� .

5. �� , �� (Initializing a Member Array). �� (initialization list) � ��, �� .

� �� weekdays.cpp �� 20 �� day_name �� weekday. �� . �� , �� ��  � �� :

// FIRST INCORRECT construction
class weekday
{
private:
    // no good
    char day_name[DPW][MAX] = { "Sunday",    "Monday",   "Tuesday",
                                "Wednesday", "Thursday", "Friday",
                                "Saturday"};

. . .

}; // end of class weekday

��

Cannot initialize a class member here.

// SECOND INCORRECT construction
class weekday
{
private:
char day_name[DPW][MAX]

public:
    // no good!!!
    weekday() : day_name[0]("Sunday"),   day_name[1]("Monday"),
                day_name[2]("Tuesday"), day_name[3]("Wednesday"),
                day_name[4]("Thursday"), day_name[5]("Friday"),
                day_name[6]("Saturday")
    { }

. . .

}; // end of class weekday

�� (�� , �� )

( expected.
Member 'weekday::day_name' is initialized more than once.
( expected.
Member 'weekday::day_name' is initialized more than once.
( expected.
Member 'weekday::day_name' is initialized more than once.
( expected.
Member 'weekday::day_name' is initialized more than once.
( expected.
Member 'weekday::day_name' is initialized more than once.
( expected.
Member 'weekday::day_name' is initialized more than once.
( expected.

�� , �� day_name, � �� (� �� ). �� , �� day_name[0], day_name[1] � �.�. �� day_name � �� .

�� , �� day_name �� :

class weekday                         // class of day names
{
   private:
      int day_number;                 // Sunday = 0, etc.
      static const char day_name[DPW][MAX];
. . .

}; // end of class weekday

const char weekday::day_name[DPW][MAX] = {"Sunday", "Monday",
                                          "Tuesday", "Wednesday",
                                          "Thursday", "Friday",
                                          "Saturday" };

�� , �� :

// weekdays1.cpp
// creates a class of days of the week objects

#include <iostream.h>
#include <string.h> // for stricmp()
#include <conio.h> // for getche()

class weekday                         // class of day names
{
   private:
      int day_number;                 // Sunday = 0, etc.
      static const int MAX = 10;     // maximum length of day name, +1
      static const int DPW = 7;      // days per week
      static const char day_name[DPW][MAX];

   public:
      void inday()                    // user inputs day name
      {
         char tempday[MAX];           // holds user input
         int gotit = 0;               // match found? (0=false)
         int j;                       // loop variable

         while( !gotit )              // cycle until user enters
         {                            // a correct name
            cout << "Enter day of week (e.g., Friday): ";

            cin >> tempday;
            for (j = 0; j < DPW; j++)      // compare user input
            {                              // with list of names
               if (stricmp(tempday, day_name[j]) == 0)
               {                   // if there's a match,
                  gotit = 1;          // set flag,
                  break;              // break out of for loop
               }
            } // end for

            day_number = j;           // record what day it was
         } // end while
      } // void inday()

      void outday()                   // display the day name
      {
         cout << day_name[day_number];
      }

      void outnumber()                // display the day number
      {
         cout << (day_number + 1);
      }

      void add(int days)             // add days to
      {                              // this weekday
         day_number += days;         // add days
         day_number %= DPW;          // ensure not > 7
      }
}; // end weekdays class

////////////////////////////////////////////////////////////////
void main()
{
weekday wd; // make a weekday object

cout << "What day is it?" << endl;
wd.inday(); // user gives it a value

cout << "You entered ";
wd.outday(); // display its day name

cout << "\nThat's day number ";
wd.outnumber(); // display its day number

   wd.add(10);                      // add 10 days to it
   cout << "\nTen days later is ";
   wd.outday();                     // display its day name

// stop the flow on the monitor
getch();

} //end main

�� , �� MAX � DPW �� :

static const int MAX = 10; // maximum length of day name, +1
static const int DPW = 7; // days per week

�� 28 �� .
.

^{(��)}
.
�� .
[1] Robert Lafore; C⁺⁺ Interactive Course. Waite Group Press, Macmillan Computer Publishing, 1996.
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��: ��. �� .
[ �� 33 �� 2009 � �� "��" www.kosnos.com ]

Keywords: �++, OOP programming , C++ , Classes , Inheritance , Reusability , Creating New Data Types , Polymorphism and Overloading
�� : �� , ��, �� , �� switch if else ?
Arrays as Instance Data
Array Sized with Constant
Static Constant Variables
The enum Hack
Arrays Sized at Compile Time
Initialization Is Not Assignment
Instance Data Initialization