cs201/04 -- Objects
- object::gloss="A collection of pieces of data that has operations defined on it",
all objects in C++ belong in a class that defines the type of data and what you
can do to it.
2.6 Strings
-
A vital, common, useful class of objects are strings.
Strings will appear in quizzes, labs, classes, projects,
the final, and most real programs you write.
- member_function_call::= object "." function_name "(" list_of_parameters ")".
my_name . length()
my_name . substr(0,1)
2.6.3 Concatenation
Advanced Topic 2.6 -- Old fashioned strings and chars
We will review this later. - character_literal::="'" char "'".
'a'
'\n'
Examples -- initials
[ initials.cpp ]2.6.4 Formatted Output
The library named iomanip is a complex and complete library of functions that change the format of input and output. I usually cover it in detail in CSCI202. But if you want a reference see [ ../cs202/iomanip.html ] for all the details in a terse format.Notes on strings
[ string.html ]
2.6.1 String Variables
string variable;
Sets variable to the empty string.string variable = "initial value";
Notice that the first character in a string is numbered zero
2.6.3 Substrings
Table 4 String Functions
Take note of these.Syntax 2.9 Member function call
. . . . . . . . . ( end of section 2.6 Strings) <<Contents | End>>
Why we have objects and how they work
The watch analogy.Example 1 -- string
TableString member functions Returns s.length() int s.substr(start) string s.substr(start, number) string
(Close Table)
2.7 Using Objects
Objects are an important way to make complex programs easier to understand and change. The example classes of objects: Time, Employee, Point, Line, Circle, ... are not part of standard C++. They will be used to make some labs more entertaining. The may enrich some classes.Objects have
- Constructors -- make new objects
- Mutator functions -- change existing objects
- Accessor functions -- return properties of existing objects
- Destructors -- behind the seen tidying up of old objects
2.7.1 Time Objects
Syntax 2.10 Object Construction
- member_function_call::= object "." function_name "(" list_of_parameters ")".
- object_construction::=class_name ( parameters )| class_name ( ).
Time()
Time(10,0,0)
Employer("Richard Botting", 80000)Point(1,2)
Syntax 2.11 Object Variable Definition
- object_variable_declaration::= class_name variable_name ( parameters ) | class_name variable_name.
Time now;
Time class(10,0,0)
Employer me ("Richard Botting", 80000)Point origen(0,0);
Table 5 Member Functions of the Time Class
Take note.
TableExample Type Purpose Time() constructor Makes an object for the current time Time(h,m,s) constructor Makes the time with hours h, minutes m, and seconds s t.get_seconds() accessor return number of seconds in t t.get_minutes() accessor return number of minutes in t t.get_hours() accessor return number of hours in t t.add_seconds(n) mutator changes t to n seconds later t.seconds_from(t2) accessor return the number of seconds between t and t2
(Close Table)
example on page 73 ch02/time.cpp
[ time.cpp ]Example time2.cpp
[ time2.cpp ]Common Error 2.7 -- Wot -- No object
2.7.2 Employee Objects
[ employee.cpp ]Table 6 Member Functions of the Employee Class
TableExample Type Purpose Employee(n,s) constructor makes a new employee with name n and salary s e.get_name() accessor returns the name of e. e.get_salary() accessor returns the salary of e. e.set_salary(s) mutators changes the salary of e
(Close Table)
2.8 Displaying Graphical Shapes
2.8.1 Graphic Objects -- Point Circle Message Window
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We have a version of Horstmann's Graphic library in
/share/ccc3e
we also have to include the windowing library called "X11R6" in our code. So a typical compilation looks likeg++ -w -I/share/ccc3e -I/usr/X11R6/include -I/usr/include -L/usr/X11R6/lib -lX11 -o lab03/message lab03/message.cpp /share/ccc3e/ccc_x11.cpp /share/ccc3e/ccc_shap.cpp
The good news is that "Q" does this for you if you "#include" the ccc library. The above command was run when I typed
Q lab03/message.cpp
Note that it is much easier to do graphics programs in C++ in our labs rather than remotely. You need a working local C++ compiler and the Horstmann CCC library installed.
Table 7 Point Class
Table 8 Circle Class
Table 9 Line Class
The default coordinate system in ccc
![[Grid showing coordinates in default ccc window]](img1.gif)
Random Fact 2.2 Computer Graphics
My Ph. D. topic -- The fundamental algorithms of Computer Graphics.The secret of computer graphics is the Cartesian Geometry invented by Rene Descartes, where each point in the picture or on the screen is given a pair of numbers (called x and y coordinates).
Consequence: computer graphics includes a lot of mathematics.
2.8.2 Choosing a Coordinate System
2.8.3 Getting Input from the graphics window
Table 12 GraphicsWindow
Refer to this when writing graphic code.For Your Information -- A Picture of the ccc Graphics Library
![[A Unified Modelling Language model of the ccc library]](ccc.gif)
Previous -- Numbers
[ 03.html ]Project 1 Due at start of class
[ projects.html#P1 ]Study pages 62 to 86 inclusive
-
Computers handle non-numeric data.
These are called objects in C++.
. . . . . . . . . ( end of section 2.8 Displaying Graphical Shapes) <<Contents | End>>
Review Questions
Try to do as many of these questions as you have time for: R2.8, R2.9, R2.10, R2.11, R2.12, R2.13, R2.14, R2.15, R2.16, R2.17, R2.18, R2.19, R2.20, R2.21.Write up and hand in one of these exercises and your solution, with your name, for me to grade, before the start of class.
Exercises on data types
[ av03b.cpp ] (review tracing), [ av03.cpp ] and [ av03a.cpp ] (String operations and tracing), [ av03c.cpp ] (substrings), [ av03d.cpp ] (concatenation), [ av03e.cpp ] (concatenation substring and length).Programming Problem: you need to input a phone number from the user in format "123-456-7890" and extract and output the area code("123") and the seven digit phone number("4567890").