Copyright © 2002-2008 Curt Hill Structured Data What this course is about

Copyright © 2002-2008 Curt Hill

Structured Data

What this course is about

Last class• The first semester is mostly about:• Common syntax• Executable statements• Flow of control• Functions• This is stuff that is in every

programming langauge• This course is mostly about

structured data



Un-Structured Data• The simple types are not structured:

– bool– char– double– float– int

• One name and one value• Usually reserved words in C/C++/Java


Memory models• A running program has several segments

of memory• The code segment

– Machine language instructions– Some types of constants

• The stack segment– Local and global variables– Temporary values

• Return addresses and values• Temporary expression values

• Heap– Dynamically allocated variables– Allocated and freed explicitly by the

programmer


Structured Data• One item with multiple values• Data thingies clustered together• Ability to access as a whole• Ability to access the individual

values• Always shows relationship of the

values to one another


The structured data types• Arrays• Structs• Unions• Classes• Files• Pointers• Dynamic data structures


Arrays• Every language has one• Homogeneous data structure• Many values with just one type• Identical form and function

– Interchangeable values– Sortable

• Different in C/C++ than others• Example:

– Test scores

87

69

72

95

76

86


Structs• Same as:

– Pascal record– COBOL group

• Heterogeneous data structure• Many values and many types• Collection of attributes• Example of a person:

– Age (int)– Wage (float)– Name (character string)– Gender (bool)

Bill Smith

35

9.65

true


Unions• Different ways to treat the same

memory• A cast converts from one type to an

equivalent value in another type• Unions do not cast, they use the same

memory in one of several ways• Example of marital status from a

personnel record– If married save the spouse name– If divorced save the divorce date– If single save whether a dependent– The first byte of each is exactly the same

memory byte


Classes• Only one not in C• Basis of object oriented

programming in C++ and Java• Struct as an independent item• Extension of a struct with

– Visibility– Member functions, often called

methods (these did exist but were not often used in structs)

– Inheritance– Polymorphism

Copyright © 1998-2008 - Curt Hill

Importance of classes• The difference between the OO

languages and previous– Main difference between C and C++

• Objects become our main abstraction tool– Previously functions were

• They allow us to divide our programs into bite size pieces

• They facilitate reuse• They simplify design

Classes• We will take four shots at the class• Simple definitions• More complicated with operator

overloads• Inheritance and polymorphism• Generics – template classes

– This will lead to the Standard Template Library in the next semester



Files

• Arrays on disk and not in memory• Only permanent data structure• Not a machine dependent item but

an Operating System dependent item

• Example– File of scores

87

72 87908379 77918982


Pointers• An address to a memory location• In C/C++/Pascal must point at only

one type• Changing the pointer is different

than changing the item pointed at• In C/C++ can be automatically cast

to an int• The mechanism used for dynamic

allocation• Intertwined with arrays


Dynamic data structures• A technique using both pointers

and some other structured type– Usually a class– May be an array or struct

Documents

Copyright © 2002-2008 Curt Hill Structured Data What this course is about