• 2 pts: Attendance(at start and end of lab)
• 8 pts: Participation

Lab Objectives

To gain experience in

• using objects
• constructing objects and supplying initial values
• using member functions and the dot notation
• modifying and querying the state of an object through its member functions
• writing simple graphics programs containing points, lines, circles and text.
• selecting appropriate coordinate systems
• processing user input and mouse clicks in graphics programs
• developing test cases that validate the correctness of your programs

Review 1. Constructing Objects

Declaring an object to store information is like declaring a variable of numeric data type. For instance

int counter; /* makes an int */
Time  lunch_time; /* makes a Time object */

While both of these statements declare a new variable, there is a difference in how each is initialized. When declaring counter, the value will be whatever is leftover from that memory location's last use. It is suggested you initialize counter when declaring it like this, int counter = 0; to avoid this problem.

Objects are initialized when they are defined, based upon the object type. Time objects are initialized to the current time. If you don't want to initialize an object with the default, you supply construction parameters. For example, you can construct a Time object by specifying hour, minute and second, for example Time (11,20,0)

To what values is a Time object set by Time new_time = Time()

Initialize a Time variable to the time you usually get up.

What is the outcome of constructing a Time object with

Time next_date(Saturday, 18, 0, 0);

What is the outcome of Time next_date = 6:00pm?

What is the difference between Time next_date(18, 0, 0) and Time next_date = Time (18, 0, 0);

Review 2. Using Objects

An object's member functions are applied to a particular instance of an object type using the dot-notation. For example, time_var.get_seconds() returns the number of seconds stored in a particular Time object called time_var. Member functions that return stored information when applied to an object are called accessors, those that change the stored information are called mutators.

Given two instances of the Time class, the beginning and end of a typical workday:

tstart = Time(9,0,0)
tend = Time(17,0,0)

What is the result of each of the following:

cout << tstart.get_hours() << " / " << tstart.get_minutes()

tend.add_seconds(1200);

tend.seconds_from(tstart);

Review 3. Real Life Objects

A direct and natural comparison can be made between an object and the entity that it represents. For example, here is how you might construct and access objects of an Address class:

Address a(number, street_name, street_type);
a.get_number();
a.get_street_name();
a.get_street_type();

Personal information about an individual would be another common example. Give a constructor and corresponding accessors for personal information having the following form:

Serdni Vasnar
096-33-2123
December 30, 1949

Grachics Objects

Instructions for using the graphics objects in lab:

To use the graphics objects provided by the author of our textbook, we will need to do a few things differently from what you have learned.

• You need to include the header file ccc_win.h at the top of your program.
  
  #include "ccc_win.h"
  
  Note that you do NOT use the < > but use " " around the filename instead.
  
  
• The entry point to your program must be ccc_win_main instead of main.
  
  

         int ccc_win_main()
         {
            // your code goes here
            return 0;
         }
         

• To compile your graphics program, you need only type:
  
  compile
  
  at the command prompt after saving your program. You do not type g++ source_file.cpp.
  
  
• To run your program, you will need to type:
  
  main
  
  at the command prompt instead of a.out.
  
  
• To display the graphical objects, you cannot use the iostream library for input/output from/to the cin and cout streams. Instead, you will send output to the graphics window using cwin.
  
  To output a circle to the graphics window cwin:
  
  

         Circle c;
         cwin << c;   // Do NOT use cout << c;
         

  For more info on this, see Input/Output to Graphics Window below.
  
  
• As was suggested with your other programs, you now must call your source file, main.cpp.

Graphic Objects and their member functions:

Below is a reference to all the objects provided in the ccc_win library and their member functions.

Point

The Point is simply a ( x, y ) pair representing a coordinate in the window.

If you wanted to create a point in the center of the default drawing area and then move it 3 units to the left, your code might look something like the following:

    Point my_point( 0, 0 );
    my_point.move( -3, 0 );
    

Circle

A Circle is defined by a Point and a radius.

Line

A line simply joins 2 end Points. The Line object differentiates between the starting Point, p, and the ending Point, q.

Message

Message objects are used to display text and numbers in the graphics window. You can create a Message object using either a string or a numeric type such as int or double.

Input/Output to Graphics Window

To display objects in a graphics window, use the following functions of the GraphicWindow class. The GraphicWindow object, w, in this table will be cwin in your programs.

Graphics Structures

Program 1. Line

Write a program that uses five Line objects to draw a pentagon, like this:

Program 2. Lines and Circles

Use Circle and Line objects to draw a train engine like this :

Program 3. Moving graphical objects

Generate five circles with center (0,0) and radius 1, 2, 3, 4, and 5. Use the move method of the Circle class to draw the circles all tangent at a common point, like this:

Choosing a Coordinate System

Program 4. Comparing coordinate systems

Write a program that changes the default coordinate system to a coordinate system where the upper lefthand corner is (0,0) and the lower righthand corner is (3,3). Then draw a stopsign like this:

Change the program to display the same stopsign in a coordinate system with upper left = (-2.5, 1.5) and lower-right = (1.5, -3.5).

Which coordinate system was easier for you to work with? Why?

Program 5. Zooming out

Modify the phoenix.cpp program of the textbook to display the points in a zoomed-out coordinate system, that is, the curve should look as though it is being viewed from a greater distance, but still be centered, like this:

#include "ccc_win.cpp"

int main()
{  
   cwin.coord(1, 33, 12, 11); // only change this line!!!

   cwin << Point(1, 11);
   cwin << Point(2, 12);   
   cwin << Point(3, 16);   
   cwin << Point(4, 20);   
   cwin << Point(5, 25);   
   cwin << Point(6, 31);   
   cwin << Point(7, 33);   
   cwin << Point(8, 32);   
   cwin << Point(9, 29);   
   cwin << Point(10, 23);   
   cwin << Point(11, 16);   
   cwin << Point(12, 12);
   
   return 0;
}

Program 6. Getting Input from the Graphics Window

Write a program that 1) gets two mouseclick points from the user 2) draws a rectangle with the coordinates of the clicks as upper-left and lower-right corners, 3) prompts for the user's name and 4) draws the name inside the rectangle.