ObjectOriented Programming Using C Third Edition

1
Object-Oriented Programming Using CThird
Edition

• Chapter 5
• Understanding Arrays, Strings, and Pointers

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Objectives

• Learn about memory addresses
• Learn about arrays
• Store values in an array
• Access and use array values
• Avoid common errors with arrays
• Learn techniques to access part of an array

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Objectives (continued)

• Use parallel arrays
• Use arrays of objects
• Learn how to use strings
• Discover special string-handling problems
• Learn about pointers
• Use a pointer in place of an array name

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Understanding Memory Addresses

• Each location where a piece of data can be stored
  is identified by a memory address
• When you declare a variable with a statement such
  as int myAge
• The computer chooses an available memory location
• Associates the name myAge with the memory address
  of that location

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Understanding Memory Addresses (continued)
Address operator
Address appears as a hexadecimal number
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Understanding Arrays

• Array list of items that all have the same type
• Subscript number that indicates the position of
  the particular array element being used
• Element single object in an array
• double moneyCollected5

Reserves sizeof(int)5 bytes of memory
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Understanding Arrays (continued)

• int someNumbers7
• If you access someNumbers7, you may get a
  warning or a garbage value

coutltltsomeNumbers produces the same output as
coutltltsomeNumbers0
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Storing Values in an Array

• int rent4
• rent0 250
• rent1 375
• rent2 460
• rent3 600
• int rent4 250, 375, 460, 600
• int rent 250, 375, 460, 600
• int rent4 250, 375
• int rent3 250, 375, 460, 600
• int rent4 0

rent2 and rent3 are set to 0
Syntax error
Sets all array elements to 0
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Accessing and Using Array Values
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Accessing and Using Array Values

• You can also use a variable as a subscript

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Accessing and Using Array Values (continued)
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Avoiding Common Array Errors

• When working with arrays, common errors include
• Forgetting that arrays are zero based

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Pitfall Accessing Locations Beyond the Array
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Using Part of an Array
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Using Part of an Array (continued)

• Tip You cannot use a variable to declare an
  arrays size you must use a constant

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Using Parallel Arrays

• Parallel arrays are corresponding arrays in which
  values in the same relative locations are
  logically related

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Using Parallel Arrays (continued)
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Using Parallel Arrays (continued)
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Using Parallel Arrays (continued)
Flag could also be of type bool
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Creating Arrays of Structure Objects
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Using Strings

• String value expressed within double quotes
• You can type two characters within single quotes
  when they represent a single character \n
• Hello is a string constant
• To store a value such as Hello, you must create
  a string variable in one of two ways
• Create a string as an array of characters
• Create a string using the string class defined in
  the C standard library

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Strings Created as Arrays of Characters

• char firstName Mary
• char firstName Mary
• char firstName5 Mary
• char firstName5 Mary
• char firstName5 'M', 'a', 'r', 'y', '\0'
• coutltltfirstName // displays Mary
• coutltltfirstName1 // displays ary

Null character. You could also use the constant
NULL, defined in iostream
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Special String-Handling Problems When Using
Character Arrays

• Some problems occur when strings are declared as
  character arrays and you
• Try to input a string value that includes
  whitespace
• Try to assign one string to another using the
  assignment operator
• Try to compare strings using the comparison
  operator
• Exceed the bounds of an array

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Pitfall Trying to Input a String Value Including
Whitespace
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Pitfall Trying to Input a String Value Including
Whitespace (continued)
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Pitfall Trying to Assign One String to Another
Using the Assignment Operator

• char clubPresident10 Eric
• clubVicePresident10 Danielle
• Alternative 1 (does not work as expected)
• clubPresident clubVicePresident
• Alternative 2 (tedious)
• clubPresident0 clubVicePresident0
• clubPresident1 clubVicePresident1
• clubPresident2 clubVicePresident2
• Alternative 3 (must include string.h)
• strcpy(clubPresident, clubVicePresident)

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Pitfall Trying to Compare Strings Using the
Comparison Operator

• Alternative 1 (does not work as expected)
• if(clubPresident clubVicePresident)
• coutltltThey are the sameltltendl
• Alternative 2 (tedious)
• if(clubPresident0 clubVicePresident0
  clubPresident1 clubVicePresident1. . .
• Alternative 3 (must include string.h)
• strcmp(firstName, secName)

A return value of 0 indicates they are equal
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(No Transcript)
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Pitfall Exceeding an Arrays Bounds
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Pitfall Exceeding an Arrays Bounds (continued)
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An Introduction to the string Class
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An Introduction to the string Class (continued)
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Using Pointers

• Pointers variables that can hold memory
  addresses
• A pointers type indicates the type of variable
  that has an address the pointer can hold
• For example,
• int aPointer
• int myValue
• aPointer myValue
• coutltltmyValue //outputs contents of myValue
• coutltltaPointer //outputs contents of myValue
• coutltltmyValue //outputs address of myValue
• coutltltaPointer //outputs address of myValue

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Using a Pointer Instead of an Array Name
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Using a Pointer Instead of an Array Name
(continued)
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You Do It Using an Array
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Understanding Memory Addresses
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Summary

• Each location where a piece of data can be stored
  is identified by a memory address
• A list of individual items that all have the same
  type is called an array
• A subscript indicates the position of an array
  element
• You can initialize an array when you declare it
• You can access an individual array value just as
  you would access any variable of the same type

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Summary (continued)

• Common errors when using arrays include
• Forgetting that arrays are zero-based
• Forgetting that the highest legitimate subscript
  is one less than the array size
• Use a for loop to access all array elements
• Parallel arrays contain corresponding elements
• You can create arrays of structure objects

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Summary (continued)

• A C value expressed within double quotes is
  commonly called a string
• You can create a string variable
• As an array of characters
• With the string class from the C standard
  library
• Pointers are variables that hold memory addresses
• To indicate a pointer, begin the variables name
  with an asterisk