Transcript CPS120: Introduction to Computer Science

CPS120: Introduction to
Computer Science
Lecture 16
Data Structures, OOP &
Advanced Strings
Pointer Use in C++.
A pointer is a variable or constant
that holds a memory address
a) Hexadecimal numbers are used for
representing memory locations
216793
216794
216801
…
216801
216802
3
i
iptr
Using Pointers
Pointers must be initialized
e.g. iptr =&I;
This reads iptr is assigned the address of i
Intializing Pointers
Declare pointers before use, as with
other variables.
Each variable being declared as a
pointer must be preceded by an
asterisk (*).
Initialize pointers before use to a 0,
NULL or an address to prevent
unexpected results
Pointer Operators
& is the address operator which
returns the address of its operand
* is the indirection operator or
dereferencing operator and returns
the value to which the operand
(pointer) points.
sizeof - used to determine the size of
an array during program compiliation
Using enum
enum allows you to create your own simple
data types for special purposes
Create a type
Give it a name
Specify values that are acceptable
enum sizes {small, medium, large, jumbo};
The compiler assigns an integer to each enum
item
typedef
typedef gives a new name to an
existing data type
typedef float real;
Confusing to the reader, should be
used sparingly
Structures
Structures group variables together in
order to make one's programming task
more efficient.
Any combination of variables can be combined
into one structure.
This is a useful and efficient way to store data.
struct Student
{
string socSecNum;
string lastName;
string firstName;
int pointsEarned;
double gpa;
};
Using Structures
Each of the different variables are called
members of the structure
Structures allow us to keep related data
referring to individual members together
Strings, integer, and floating-point
variables may be grouped together into one
structure.
In effect, we have created our own customized
data type.
The semicolon after the closing curly brace
is required
Using the new data structure
The structure definition should be placed
above the main function of a program but
below the compiler directives
Declare an actual variable of this
programmer-created data type within a
function (such as main) in order to make
use of this structureDone with a
declaration statement like
Student freshmen;
This reates a variable called freshmen of
the data type Student
Assigning values to the structure
To assign a grade point average (GPA) of
3.4 to the gpa member of the variable
freshmen, use the statement:
freshmen.gpa = 3.4;
The period (.) that is used between the
variable name freshmen and the member
gpa is called the dot operator.
The dot operator simply us to reference
individual members of a structure
Nested Structures
You can use a previously defined structure as a member of another
structure
Address is nested inside of the Customer structure.
Since Address is used within Customer, the structure definition for
Address must be placed above Customer in order to avoid compile
errors
struct Address
{
string street;
string city;
string state;
int zip;
};
struct Customer
{
string name;
string phone;
Address homeAddress;
Address businessAddress; };
CPS120: Introduction to
Computer Science
Lecture 16B
Object-Oriented Concepts
The Procedural Paradigm
The functions and algorithms are the
focus, with data viewed as something
for the functions to manipulate
Object-Oriented Paradigm
Data should be placed inside the
objects and that these objects should
communicate with each other in the
form of messages
Classes
The definition of an object is know as a
class
It is similar to using basic data structures in
C++
When you declare an object, you are said
to have instantiated it (given it instances)
Objects are members of a class
Paul Millis, George Bush and George Washington
being members of the human being class
The design of a class is as important as its
implementation
Including Classes in C++
For classes, the #include directive
uses different punctuation for
header (.h) files
Quotation marks are used when the
header file is a source file in the same
location as the program source code
Angle brackets are used when the
header file is one of the compiler's precompiled library functions
Designing a Class
Think in an object-oriented way
E.g. an answering machine encapsulates
the functions of an answering machine
with the data (messages).
The buttons are the equivalent of sending
messages to the machine
Defining a Class
Functions and variables that are
prototyped and declared in a class
definition are called members
Public vs Private
Private: Cannot be accessed outside the
object
Public: Can have access to all the
variables and functions
public:
// constructors
circle();
// default constructor
circle(const circle &); // copy constructor
// member functions
void SetRadius(float);
double Area();
private:
// data
float radius;
Constructors
Allow all data encapsulated within an
object to be initialized to preset values
so that errors can be avoided
Member Functions
Provide a way for a programmer to
pass data to and get data from an
object
Implemented like a normal C++
function
Except -- The class name and the scoperesolution operator (: :) precede the
function name
circle : : circle() // default constructor
OOP Advantages: Reusability
Reusability is a major benefit of objectoriented programming
OOP Advantages: Containment
Containment is a term used to describe
an object that contains one or more
objects as members
(Passes the 'has-a' rule)
OOP Advantages: Inheritance
Inheritance is the term used to describe
an object that inherits properties from
another object
(Passes the 'is-a' rule)
The class from which an object inherits
properties is called a parent class or
base class
The class that inherits the properties is
called a child class or derived class
CPS120: Introduction to
Computer Science
Lecture 16C
Advanced Strings
Library functions manipulate strings
length function
stringLength = userString.length( );
To compare two strings
if (string1 = = string2)
Test two strings alphabetically
if (string1 < string2)
{
cout << "string1 comes before string2
alphabetically ";
}
Library functions manipulate strings
To compare two strings
if (string1 = = string2)
Library functions manipulate strings
Test two strings alphabetically
if (string1 < string2)
{
cout << "string1 comes before
string2
alphabetically ";
}
Concatenation
To combine two strings into one larger string:
name = "John";
lastName = "Doe";
cout << name + lastName;
The character array that is going to receive
the additional characters must have enough
memory allocated to hold the additional
characters
The STRCAT function will continue to add
characters even if it reaches the end of the
destination character array
The result is that other memory is overwritten
with the remaining string data.
A String Class
A string class can make C++ strings
much easier to use
a) A string class can provide bounds
checking to avoid string errors
b) A string class can also allow the
use of standard C++ operators when
working with strings
i)
+, =, and = =
Converting Strings
There are C++ library functions that
allow you to convert numbers stored
in strings to integer and floating
point values
atoi-- numbers stored as characters can
be converted for calculations
atol -- converts a string to a long integer
atof -- convers a string to a floating
point number
Using A String Class
Required header file
#include "oostring.h"
Instantiating a String Object
// Instantiate empty string object
oostring MyString1;
// Initialize while instantiating
oostring MyString2("Hello, World!");
Assigning Values to Strings
MyString1 = MyString2;
MyString1 = "string variable";
MyString1 = 'A';