Lecture 8: A Simple System
 Software Engineering:

Class
• member variables/functions
• constructor (function)

A simple system -elevator
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Classes and Abstract Data Types(ADT)
 Structures: A data type with many member
variables
 Classes: A data type with many member
variables and member functions.
 ADT: Data types users know functionality of
public member variables and member functions
but not necessary the implementation details.
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Class
 A class is similar to a data type and an object in
a class is similar to a variable in a data type.
 A class may have

associated member variables which is accessed via a dot after
the name of the object and the variable name after the dot.


Example: obj1.x1 or obj1.array[6]
associated member functions which is accessed via a dot
after the name of the object and the function name after the dot and
parameter list in parenthesis after the function name.

Example: obj1.f(x1,x2)
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 public member variables/functions: can be
accessed in any function
 private member variables/functions: can only
be accessed in member functions of the same
class.
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Syntax for Prototype a Class
class class_name{//prototype a class
public:
//public functions and variables
double a_function(); //prototype a member function
int i;
//prototype an int
private:
//private functions and variables no other
//functions can access it except of the same class
void auxi_function(); //an auxiliary function
long another_variable;
//private int
};//end definition with semicolon;
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class StudentRecord{//example of prototype class
public:
//so that other functions can access it.
double final(); //prototype of member function
void print_out();
//prototype output member function
void get_scores();
//prototype input member function
private:
//no other functions can access
//it except in the same class
long int ID;
//student id is long integer
int score1, score2, exam;
//scores of hmwk 1,2, exam
double w1=0.25, w2=0.25, w3=0.5;
};//end definition with semicolon;
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Syntax for define member functions
Return_type class_name:: function_name()
{
//statements of what to do with the function;
//member variables and functions may be used
//additional auxiliary variables may also be defined
//and used
}
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
void StudentRecord:: get_scores(){

cout << “enter student ID” <<endl;
cin >> ID;
//use of member variable
cout << “enter his scores in hmwk1, hmwk2, exam\n”;
cin >> score1>>score2>>exam; //use of member variables
}

void StudentRecord:: print_out() {





cout << “Final score of ”<<ID<<“ is ”<<final()<<endl;
//member variable is used.
}

double StudentRecord::final()


• {//member function definition
• return (w1*score1+w2*score2+w3*exam);
• //member variables are used}
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 Initialization with constructors:


class StudentRecord{
public:
//so that other functions can access it.
•
•
•
•
•

double final();
//prototype of member function
void print_out();
//prototype output member function
void get_scores(); //prototype input member function
StudentRecord(long id,int mark1, int mark2, int mark3);
//a constructor prototype;
private:
• long int ID;
//student id is long integer
• int quiz, lab_work, exam; //marks for them
• double w1=0.2, w2=0.2, w3=0.6;
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};
//end definition with semicolon;
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 Calling a constructor:


class_name Obj_name(arguments for constructor);
Object=class_name(arguments for constructor);
 Default constructor:

class_name();//definition
 Calling default constructor:


class_name Obj_name;
Object=class_name();
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 #include <iostream.h>
 #include <student.h>
 main(){StudentRecord x(971423,80,80,60);//constructor is

// called according the following definition.
 x.print_out();
 return 0;}
 StudentRecord::StudentRecord(long id,int mark1, int mark2, int mark3)
 {ID=id;
 quiz=mark1;
 lab_work=mark2;
 exam=mark3;

}
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



#include <iostream.h>
#include <student.h>
char anymore();
//prototype
main(){char more; StudentRecord x;

do {
• x.get_scores();
• x.print_out();
• more=anymore();

//can be accessed in main() since it is
//a public function
//the same reason as above
} while (more= =‘Y’);
 return 0;}
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A simple System-an elevator system
 Define a class for an elevator




array[6]- for the 6 floors of the building, if a person
press ‘i’ in the elevator, then array[I-1] is set to be 1.
sign-indicates the elevator is going “up” or “down”.
k- the present position of the elevator.
count-the number of stops in this round.
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A simple System-an elevator system(continued)
 Description of the system:

there are two (or three) elevators to serve the
building
 Control strategies:


when an elevator reaches a level, it will test if stop
is required and will stop if yes.
To balance the number of people/number of stops,
we use count to remember the number of times it
stopped in this round (from 1 to 6 or from 6 to 1).
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