Composite Data Types

1
Composite Data Types

2
Topics to be Covered

• Abstract data types
• One-dimensional arrays
• Two-dimensional arrays
• Records

3
Data Abstraction

• Separation of a data types logical properties
  from its implementation.

LOGICAL PROPERTIES IMPLEMENTATION
What are the possible values? How can
this be done in C? What operations will be
needed? How can data types be used?
4
Data Encapsulation

• is the separation of the representation of data
  from the applications that use the data at a
  logical level a programming language feature
  that enforces information hiding.

int y y 25
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Encapsulated C Data Type int
TYPE int
Representation of int as 16 bits twos
complement Implementation of
Operations
Value range INT_MIN . . INT_MAX
Operations prefix - prefix
infix - infix infix / infix
infix Relational Operators infix
(inside)
6
Abstract Data Type (ADT)

• A data type whose properties (domain and
  operations) are specified independently of any
  particular implementation.

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Data Structures

• A collection of data elements
• that can be decomposed into its component
  elements
• whose organization is a feature how each element
  is accessed.
• that its implementation of both organization and
  accessing of data elements in an ADT

8
Data from 3 different levels

• Application (or user) level modeling real-life
  data in a specific context.
• Logical (or ADT) level abstract view of the
  domain and operations. WHAT
• Implementation level specific representation of
  the structure to hold the data items, and the
  coding for operations. HOW

9
Viewing a library from 3 different levels

• Application (or user) level Library of Congress,
  or Baltimore County Public Library.
• Logical (or ADT) level domain is a collection of
  books operations include check book out, check
  book in, pay fine, reserve a book.
• Implementation level representation of the
  structure to hold the books, and the coding for
  operations.

10
Viewing a ATM Machine from 3 different levels

• Application (or user) level
• Logical (or ADT) level
• Implementation level

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Composite Data Type

• A composite (or structured) data type is a type
  which
• stores a collection of individual data components
  (values) under one variable name,
• and allows the individual data components to be
  accessed for assignment or use.

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4 Basic Kinds of ADT Operations

• Constructor -- creates a new instance (object) of
  an ADT.
• Transformer -- changes the state of one or more
  of the data values of an instance.
• Observer -- allows us to observe the state of one
  or more of the data values without changing them.
  
• Iterator -- allows us to process all the
  components in a data structure sequentially.

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13
Two Forms of Composite Data Types
STRUCTURED

• UNSTRUCTURED

The organization determines method used to
access individual data components.
Components are not organized with respect to
one another.
EXAMPLES EXAMPLES arrays classes and structs
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14
C Built-In Data Types
Simple
Composite
Integral
Floating
array struct union class
char short int long enum
float double long double
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One-Dimensional Array at the Logical Level

• A one-dimensional array is a structured composite
  data type made up of a finite, fixed size (known
  at compile time) collection of homogeneous (all
  of the same data type) elements having relative
  positions and to which there is direct access
  (any element can be accessed immediately).
• Array operations (creation, storing a value,
  retrieving a value) are performed using a
  declaration and indexes.

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Implementation Example
This ACCESSING FUNCTION gives position of
valuesIndex Address(Index) BaseAddress
Index SizeOfElement

• float values5 // assume element size is
  4 bytes

Base Address
7000 7004 7008 7012
7016
values0 values1 values2 values3
values4
Indexes
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One-Dimensional Arrays in C

• The index must be of an integral type (char,
  short, int, long, or enum).
• The index range is always 0 through the array
  size minus 1.
• Arrays cannot be assigned, and cannot be the
  return type of a function.
• SYNTAX
• DataType ArrayName ConstIntExpression

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Another Example

• char name10 // assume element size is 1
  byte

This ACCESSING FUNCTION gives position of
nameIndex Address(Index) BaseAddress Index
SizeOfElement
Base Address
6000 6001 6002 6003 6004 6005
6006 6007 6008 6009
name0 name1 name2 name3 name4
. . . . .
name9
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Assigning values to individual array elements

• float temps 5 // allocates memory for
  array
• int m 4
• temps 2 98.6
• temps 3 101.2
• temps 0 99.4
• temps m temps 3 / 2.0
• temps 1 temps 3 - 1.2 // what value
  is assigned?

7000 7004 7008 7012
7016
99.4 ? 98.6 101.2
50.6
temps0 temps1 temps2 temps3
temps4
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What values are assigned?

• float temps 5 // allocates memory for
  array
• int m
• for (m 0 m lt 5 m)
• temps m 100.0 m 0.2

7000 7004 7008 7012
7016
? ? ? ?
?
temps0 temps1 temps2 temps3
temps4
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Now what values are printed?

• float temps 5 // allocates memory for
  array
• int m
• . . . . .
• for (m 4 m gt 0 m-- )
• cout ltlt temps m ltlt endl

7000 7004 7008 7012
7016
100.0 100.2 100.4 100.6
100.8
temps0 temps1 temps2 temps3
temps4
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Variable subscripts

• float temps 5 // allocates memory for
  array
• int m 3
• . . . . . .
• What is temps m 1 ?
• What is temps m 1 ?

7000 7004 7008 7012
7016
100.0 100.2 100.4 100.6
100.8
temps0 temps1 temps2 temps3
temps4
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A Closer Look at the Compiler

• float temps5 // this declaration allocates
  memory
• To the compiler, the value of the identifier
  temps alone is the base address of the array. We
  say temps is a pointer (because its value is an
  address). It points to a memory location.

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Initializing in a declaration

• int ages 5 40, 13, 20, 19, 36
• for ( int m 0 m lt 5 m )
• cout ltlt ages m

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Passing Arrays as Parameters

• In C, arrays are always passed by reference,
  and is not used with the formal parameter type.
• Whenever an array is passed as a parameter, its
  base address is sent to the called function.

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Passing Arrays as Parameters

• Generally, functions that work with arrays
  require 2 items of information as actual
  parameters
• the beginning address of the array (in memory),
• and the number of elements to process in the
  array.

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const Array Parameter

• Because arrays are always passed as reference
  parameters, you can protect the actual parameter
  from unintentional changes by using const in
  formal parameter list and function prototype.
• FOR EXAMPLE . . .
• // prototype
• float SumValues( const float values ,
• int numOfValues )

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float SumValues (const float values ,
int
numOfValues )

• // Pre values 0 through valuesnumOfValues-1
  
• // have been assigned
• // Returns the sum of values0 through
• // valuesnumOfValues-1
• float sum 0
• for ( int index 0 index lt numOfValues
  index )
• sum values index
• return sum

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Array Index

• Array index can be any integral type. This
  includes char and enum types.
• It is programmers responsibility to make sure
  that an array index does not go out of bounds.
  The index must be within the range 0 through the
  declared array size minus one.
• Using an index value outside this range causes
  the program to access memory locations outside
  the array. The index value determines which
  memory location is used.

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Array with enum Index Type

• DECLARATION
• enum Department WOMENS, MENS, CHILDRENS,
  LINENS, HOUSEWARES, ELECTRONICS
  
• float salesAmt 6
• Department which
• USE
• for ( which WOMENS which lt ELECTRONICS
  
• which
  Department ( which 1 ) )
• cout ltlt salesAmt which ltlt endl

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float salesAmt 6
salesAmt WOMENS ( i. e. salesAmt
0 ) salesAmt MENS ( i. e.
salesAmt 1 ) salesAmt CHILDRENS
( i. e. salesAmt 2 ) salesAmt
LINENS ( i. e. salesAmt 3 )
salesAmt HOUSEWARES ( i. e. salesAmt
4 ) salesAmt ELECTRONICS ( i. e.
salesAmt 5 )

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Parallel arrays

• DEFINITION
• Parallel arrays are 2 or more arrays that have
  the same index range, and whose elements contain
  related information, possibly of different data
  types.
• EXAMPLE
• const int SIZE 50
• int idNumber SIZE
• float hourlyWage SIZE
  parallel arrays

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const int SIZE 50 int idNumber SIZE
// parallel arrays holdfloat
hourlyWage SIZE // related information
idNumber 0 4562 hourlyWage 0
9.68 idNumber 1 1235
hourlyWage 1 45.75
idNumber 2 6278 hourlyWage 2
12.71 .
. .
. . .
.
. . .
.
. idNumber 48 8754 hourlyWage 48
67.96 idNumber 49 2460
hourlyWage 49 8.97

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String in C

• A string is an array of characters which contains
  a non-printing null character \0 ( with
  ASCII value 0 ) marking its end.
• A string can be initialized in its declaration in
  two equivalent ways.
• char message 8 H, e, l, l,
  o, \0
• char message 8 Hello

2
35
char vs. string

• A has data type char
• and is stored in 1 byte
• A is a string of 2 characters
• and is stored in 2 bytes

3
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Recall that . . .

• char message8 // this declaration allocates
  memory
• To the compiler, the value of the identifier
  message alone is the base address of the array.
  We say message is a pointer (because its value is
  an address). It points to a memory location.

4
37
Aggregate String I/O in C

• I/O of an entire string is possible using the
  array identifier with no subscripts and no
  looping.

EXAMPLE char message 8 cin gtgt
message cout ltlt message HOWEVER
. . .
5
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Extraction operator gtgt

• When using the extraction operator ( gtgt ) to
  read input characters into a string variable,
• the gtgt operator skips any leading whitespace
  characters such as blanks and newlines.
• It then reads successive characters into the
  array, and stops at the first trailing whitespace
  character (which is not consumed, but remains
  waiting in the input stream).
• The gtgt operator adds the null character to the
  end of the string.

6
39
Example using gtgt

• char name 5
• cin gtgt name
• Suppose input stream looks like this
• J o e

total number of elements in the array
7000
J o e \0
name 0 name 1 name 2 name 3
name 4
7
null character is added
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Function get( )

• Because the extraction operator stops reading at
  the first trailing whitespace, gtgt cannot be used
  to input a string with blanks in it.
• If your strings declared size is not large
  enough to hold the input characters and add the
  \0, the extraction operator stores characters
  into memory beyond the end of the array.
• Use get function with 2 parameters to overcome
  these obstacles.
• EXAMPLE
• char message 8
• cin.get ( message, 8 ) // inputs at most 7
  characters plus \0

8
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inFileStream.get ( str, count 1)

• get does not skip leading whitespace characters
  such as blanks and newlines.
• get reads successive characters (including
  blanks) into the array, and stops when it either
  has read count characters, or it reaches the
  newline character \n, whichever comes first.
• get appends the null character to str.
• If it is reached, newline is not consumed by get,
  but remains waiting in the input stream.

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42
Function ignore( )

• can be used to consume any remaining characters
  up to and including the newline \n left in the
  input stream by get
• EXAMPLE
• cin.get ( string1, 81 ) // inputs at most
  80 characters
• cin.ignore ( 30, \n ) // skips at most
  30 characters // but stops if \n
  is read
• cin.get ( string2, 81 )

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Another example using get( )

• char ch
• char fullName 31
• char address 31
• cout ltlt Enter your full name
• cin.get ( fullName, 31 )
• cin.get (ch) // to
  consume the newline
• cout ltlt Enter your address
• cin.get ( address, 31 )

N e l l D a
l e \0 . . .
fullName 0
A u s t i n
T X \0 . . .
11
address 0
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String function prototypes inlt string.h gt

• int strlen (char str )
• // FCTNVAL integer length of string str (
  not including \0 )
• int strcmp ( char str1 , char str2 )
• // FCTNVAL negative, if str1 precedes str2
  lexicographically
• // positive, if str1 follows str2
  lexicographically
• // 0, if str1 and str2 characters same
  through \0
• char strcpy ( char toStr , char fromStr
  )
• // FCTNVAL base address of toStr ( usually
  ignored )
• // POSTCONDITION characters in string fromStr
  are copied to
• // string toStr, up to and including \0,
• // overwriting contents of string toStr

12
45

• include ltstring.hgt
• .
• .
• .
• char author 21
• int length
• cin.get ( author , 21 )
• length strlen ( author ) // What is the
  value of length ?

46

• char myName 21 Huang // WHAT IS
  OUTPUT?
• char yourName 21
• cout ltlt Enter your last name
• cin.get ( yourName, 21 )
• if ( strcmp ( myName, yourName ) 0 )
• cout ltlt We have the same name!
• else if ( strcmp ( myName, yourName ) lt 0 )
• cout ltlt myName ltlt comes before ltlt
  yourName
• else if ( strcmp ( myName, yourName ) gt 0 )
• cout ltlt yourName ltlt comes before ltlt
  myName

H u a n g \0
. . .
myName 0
H e a d i n g t
o n \0 . . .
yourName 0
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• char myName 21 Huang
• char yourName 21
• if ( myName yourName ) // compares
  addresses only!
• // That is, 4000 and 6000 here.
• . // DOES NOT COMPARE CONTENTS!
• .
• .

4000
H u a n g \0
. . .
myName 0
6000
H e a d i n g t
o n \0 . . .
yourName 0
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• char myName 21 Huang
• char yourName 21
• cin.get ( yourName, 21 )
• yourName myName // DOES NOT COMPILE!
• // What is the value of myName ?

4000
H u a n g \0
. . .
myName 0
6000
H e a d i n g t
o n \0 . . .
yourName 0
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• char myName 21 Huang
• char yourName 21
• cin.get ( yourName, 21 )
• strcpy ( yourName, myName ) // changes
  string yourName
• // OVERWRITES CONTENTS!

4000
H u a n g \0
. . .
myName 0
6000
u n g \0
H e a d i n g t
o n \0 . . .
yourName 0
50
Using typedef with arrays

• typedef int Boolean // names Boolean
  as a data type
• typedef char String20 21 // names
  String20 as an array type
• String20 myName // these declarations
• String20 yourName // allocate memory for
  3 variables
• Boolean isSeniorCitizen

5000
6000
7000
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51
Write a program that will...

• Read the ID numbers, hourly wages, and names, for
  up to 50 persons from a data file.
• Then display the ID number and hourly wage for
  any person in the file whose name is entered at
  the keyboard, or indicate that the person was not
  located, if that is the case.

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52
Assume file has this form with data for no more
than 50 persons
4562 19.68 Dale Nell 1235 15.75
Weems Chip 6278 12.71 Headington
Mark . .
. .
. . .
. .
8754 17.96 Cooper Sonia 2460
14.97 Huang Jeff
20
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Parallel arrays hold related data

• const int MAX_PERSONS 50
• typedef char String20 21 // define data
  type
• .
• .
• .
• // declare 3 parallel arrays
• int idNums MAX_PERSONS
• float wages MAX_PERSONS
• String20 names MAX_PERSONS
• // holds up to 50 strings each with
• // up to 20 characters plus null character \0

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int idNums MAX_PERSONS
// parallel arraysfloat wages
MAX_PERSONS String20 names MAX_PERSONS
idNums 0 4562 wages 0 19.68
names 0 Dale Nell idNums 1
1235 wages 1 15.75
names 1 Weems Chip idNums 2
6278 wages 2 12.71 names
2 Headington Mark .
. . . . .
. . .
. . . .
. .
. . . idNums 48 8754 wages 48
17.96 names 48 Cooper Sonia
idNums 49 2460 wages 49 14.97
names 49 Huang Jeff
22
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Two-Dimensional Array at the Logical Level

• A two-dimensional array is a structured composite
  data type made up of a finite, fixed size
  collection of homogeneous elements having
  relative positions and to which there is direct
  access.
• Array operations (creation, storing a value,
  retrieving a value) are performed using a
  declaration and a pair of indexes (called row and
  column) representing the components position in
  each dimension.

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• EXAMPLE -- To keep monthly high temperatures for
  50 states in a two-dimensional array.
  
• const int NUM_STATES 50
• const int NUM_MONTHS 12
• int stateHighs NUM_STATES NUM_MONTHS
• 0
• 1
• 2
• .
• . stateHighs 2 7
• .
• 48
• 49

0 1 2 3 4 5 6 7 8 9
10 11
66 64 72 78 85 90 99 115 98 90 88 80
row 2, col 7 might be Arizonas high for August
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Finding the average high temperature for Arizona

• int total 0
• int month
• int average
• for ( month 0 month lt NUM_MONTHS month )
• total total stateHighs 2 month
  
• average int ( total / 12.0 0.5 )
  

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const int NUM_STATES 50 const int
NUM_MONTHS 12 int stateHighs NUM_STATES
NUM_MONTHS
rows columns
STORAGE

• In memory, C stores arrays in row order. The
  first row is followed by the second row, etc.

Base Address
8000
8024
8048
. . .
12 highs for state 0 12 highs for state 1
etc. Alabama
Alaska first row
second row
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Implementation Level View
Base Address 8000
stateHighs 0 0 stateHighs 0 1
stateHighs 0 2 stateHighs 0 3
stateHighs 0 4 stateHighs 0 5
stateHighs 0 6 stateHighs 0 7
stateHighs 0 8 stateHighs 0 9
stateHighs 0 10 stateHighs 0 11
stateHighs 1 0 stateHighs 1 1
stateHighs 1 2 stateHighs 1 3
. . .
To locate an element such as stateHighs 2
7 the compiler needs to know that there are 12
columns in this two-dimensional array. At what
address will stateHighs 2 7 be
found? Assume 2 bytes for type int.
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Two-Dimensional Array Parameters

• Just as with a one-dimensional array, when a two-
  (or higher) dimensional array is passed as a
  parameter, the base address of the actual array
  is sent to the function.
• The size of all dimensions except the first must
  be included in the function heading and
  prototype.
• The sizes of those dimensions for the formal
  parameter must be exactly the same as in the
  actual array.

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Use the two-dimensional stateHighs array to fill
a one-dimensional stateAverages array

• const int NUM_STATES 50
• const int NUM_MONTHS 12
• int stateHighs NUM_STATES NUM_MONTHS
• int stateAverages NUM_STATES
• 0
• ? 1
• ? 2
• .
• .
• .
• 48
• 49

0 1 2 3 4 5 6 7 8 9
10 11
Alaska Arizona
43 42 50 55 60 78 79 80 77 72 63 40 66 64 72 78
85 90 99 115 98 90 88 80
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void findAverages ( const int stateHighs
NUM_MONTHS ,
int stateAverages )

• // Pre stateHighs 0..NUM_STATES-1
  0..NUM_MONTHS-1 assigned
• // Post stateAverages 0..NUM_STATES-1
  contains rounded average
• // high temperature for each state
• int state
• int month
• int total
• for ( state 0 state lt NUM_STATES
  state )
• total 0
• for ( month 0 month lt NUM_MONTHS
  month )
• total stateHighs state month
• stateAverages state int ( total / 12.0
  0.5 )

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63
Using typedef with arrays

• helps eliminate the chances of size mismatches
  between
• formal and actual parameters. FOR
  EXAMPLE,
• typedef int StateHighsType NUM_STATES
  NUM_MONTHS
• typedef int StateAveragesType NUM_STATES
• void findAverages( const StateHighsType
  stateHighs ,
  StateAveragesType stateAverages )
• .
• .
• .

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64
Declaring Multidimensional Arrays

• EXAMPLE OF THREE-DIMENSIONAL ARRAY
• const NUM_DEPTS 5 // mens,
  womens, childrens, electronics, furniture
• const NUM_MONTHS 12
• const NUM_STORES 3 // White Marsh,
  Owings Mills, Towson
• int monthlySales NUM_DEPTS NUM_MONTHS
  NUM_STORES
• rows columns sheets
• OR USING TYPEDEF
• typedef int MonthlySalesType NUM_DEPTS
  NUM_MONTHS NUM_STORES
• MonthlySalesType monthlySales

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• const int NUM_DEPTS 5 // mens,
  womens, childrens, electronics, linens
• const int NUM_MONTHS 12
• const int NUM_STORES 3 // White
  Marsh, Owings Mills, Towson
• typedef long MonthlySalesType NUM_DEPTS
  NUM_MONTHS NUM_STORES
• MonthlySalesType monthlySales

monthlySales370 sales for
electronics in August at White Marsh
3 STORES sheets
5 DEPTS rows
65
12 MONTHS columns