CPS120: Introduction to Computer Science

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CPS120 Introduction to Computer Science

• Lecture 16
• Data Structures, OOP Advanced Strings

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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 iptr 216801 3 i 216802
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Using Pointers

• Pointers must be initialized
• e.g. iptr I
• This reads iptr is assigned the address of i

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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

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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

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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

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typedef

• typedef gives a new name to an existing data type
• typedef float real
• Confusing to the reader, should be used sparingly

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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

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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

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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

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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

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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
  

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CPS120 Introduction to Computer Science

• Lecture 16B
• Object-Oriented Concepts

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The Procedural Paradigm

• The functions and algorithms are the focus, with
  data viewed as something for the functions to
  manipulate

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Object-Oriented Paradigm

• Data should be placed inside the objects and that
  these objects should communicate with each other
  in the form of messages

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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

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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 pre-compiled library
  functions

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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

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Defining a Class

• Functions and variables that are prototyped and
  declared in a class definition are called members

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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

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Constructors

• Allow all data encapsulated within an object to
  be initialized to preset values so that errors
  can be avoided

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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 scope-resolution
  operator ( ) precede the function name
• circle circle() // default constructor

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OOP Advantages Reusability

• Reusability is a major benefit of object-oriented
  programming

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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)

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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

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CPS120 Introduction to Computer Science

• Lecture 16C
• Advanced Strings

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Library functions manipulate strings

• length function
• stringLength userString.length( )
• To compare two strings
• if (string1 string2)
• Test two strings alphabetically
• if (string1 lt string2)
• cout ltlt "string1 comes before string2
• alphabetically "

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Library functions manipulate strings

• To compare two strings
• if (string1 string2)

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Library functions manipulate strings

• Test two strings alphabetically
• if (string1 lt string2)
• cout ltlt "string1 comes before string2
• alphabetically "

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Concatenation

• To combine two strings into one larger string
• name "John"lastName "Doe"cout ltlt 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.

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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

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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

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Using A String Class

• Required header file
• include "oostring.h"

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Instantiating a String Object

• // Instantiate empty string object
• oostring MyString1
• // Initialize while instantiating
• oostring MyString2("Hello, World!")

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Assigning Values to Strings

• MyString1 MyString2
• MyString1 "string variable"
• MyString1 'A'