Programming Fundamentals

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Programming Fundamentals

• ECE573 Data Structures and Algorithms
• Electrical and Computer Engineering Dept.
• Rutgers University
• http//www.cs.rutgers.edu/vchinni/dsa/

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Course Overview

• Objective
• To teach you how to program efficiently
• Prerequisites
• You know the basics of programming in C, C or
  Java
• Can write, debug and run simple programs in
  C/C/Java, and
• Have some simple understanding of object-oriented
  design

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What is a Good Program?

• Run correctly
• Run in accordance with the specifications
• Run efficiently
• In minimum time?
• Other constraints Memory use?
• How? Use appropriate data structures and
  algorithms
• Algorithm A precisely specified procedure for
  solving a problem
• Easy to read and understand
• Easy to debug
• Easy to modify (easy to maintain)
• Portability?

Focus
Software Engineering Building large SW
systems Reliable easy to maintain
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Programming Strategies

• Modularity
• Decompose a program into suitable small modules
• Test them before incorporating them into larger
  modules
• Management is simpler
• How to partition a large task?
• Abstraction
• A high level views of objects or functions
• ?Enables us to forget about low level details and
  concentrate on problems at hand

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Example

• Truck Manufacturer
• Computer to control engine operation

Computer
Load Sensors
CPU
Sensor interface
Fuel Control
Engine Speed
Interrupt Handler
Memory
Air Flow
Pedal Position
ROM
I/O Interface
Clock
Air Temperature
SW
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Example

• Truck Manufacturer
• Computer to control engine operation

Load Sensors
Computer
CPU
Sensor interface
Fuel Control
Engine Speed
Interrupt Handler
Memory
Air Flow
Pedal Position
ROM
I/O Interface
Clock
Air Temperature
When the accelerator pedal is 50 depressed, air
and fuel valves should be opened until the engine
speed reaches 2500 rpm
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Example

• Transportation Company
• Abstract view of a truck
• Just a means of transporting goods from point A
  to point B in the min time allowed by the road
  traffic etc.
• Specifications?
• The truck, when laden with 10 tonnes, shall need
  no more than 2 Gallons of fuel to travel100 miles
  when traveling at 60mph
• How it is achieved is irrelevant. Does not matter
  whether there is a control computer or other
  gadgets.

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Types of Abstraction

• Functional Abstraction
• Specify a function for a module, i.e.,
• This module will sort the items in its input
  stream into ascending order based on an ordering
  rule for the items and place them on its output
  stream
• Structural Abstraction
• Known as Object Orientation
• Construct software models of the behavior of real
  world items
• Truck manufacturer
• To analyze performance of his vehicle, employs SW
  model of the control computer
• He is only concerned with external behavior of
  the computer

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Objects

• Abstract Data Types
• Collection of data structure and a collection of
  functions or procedures which operate on the data
  structure
• Functions Procedures ? Methods
• Data structure and its methods ? Class
• Instance of a class ? Object
• Objects represent objects in the real world and
  appear in programs as variables of a type defined
  by the class
• OO additional Inheritance etc.
• Object orientation is a design methodology!
• Possible OO programs using C, Pascal etc.
• C provide additional compiler support for OO
  design
• This support must be provided by the programmer
  in non-OO languages

OO Terminology
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Example Collections

• Collections may be organized in many ways
• May use different program structures to represent
  them
• Yet, from an abstract point of view common
  operations may include
• Create Create a new collection
• Add Add a new item to a collection
• Delete Delete an item from a collection
• Find Find an item matching some criterion in
  the collection
• Destroy Destroy the collection

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Constructors and Destructors

• Constructors and destructors
• The create and destroy methods often called
  constructors and destructors-often implemented
  for any abstract data type
• Specific applications may require additional
  methods
• Ex join two collections
• One of the aims of good program design would be
  to ensure that additional requirements are easily
  handled

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Data Structure

• Name of a data type type of objects that belong
  to the collection class
• typedef struct collection_struct collection
• We are defining pointer to a structure
• We have not specified details of the attributes
  of the structure
• We will be able to substitute different data
  structures for the actual implementation of the
  collection
• We can declare objects of type collection

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Methods

• collection ConsCollection (int max_items, int
  item_size)
• void AddToCollection (collection c, void item)
• void DeleteFromCollection ( collection c, void
  itme)
• void FindInCollection (collection c, void
  key)
• C is not exactly the safest programming language
  in the sense of the support it provides for the
  engineering of quality software
• As we assumed that our collection object is a
  pointer to a structure, we assume the object
  which belongs to the collection are also
  represented by pointers to data structures
• Void will match any pointer
• Void highlights the deficiencies of C it
  doesnt provide the capability to create generic
  objects.

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Pre- and Post-conditions

• Formal specification requires pre- and
  post-conditions
• It is a contract between the object and its
  client
• Pre-conditions State of the program which the
  client guarantees will be true before calling any
  method
• Post-conditions State of the program that the
  objects method will guarantee to create for you
  when it returns
• C provides NO FORMAL SUPPORT for this
• Use assert function
• Express pre-and post conditions as comments with
  the method definition

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Assert man pages

• NAME assert - program verification
• SYNOPSIS include ltassert.hgt assert(expression)
• DESCRIPTION assert() is a macro that indicates
  expression is expected to be true at this point
  in the program. If expression is false (0), it
  displays a diagnostic message on the standard
  output and exits.

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/ Specification for Collection / typedef struct
t_Collection Collection Collection
ConsCollection( int max_items, int item_size
) / Construct a new Collection
Pre-condition max_items gt 0 Post-condition
returns a pointer to an empty Collection / void
AddToCollection( Collection c, void item ) /
Add an item to a Collection Pre-condition (c
is a Collection created by a call to
ConsCollection)
(existing item count lt max_items)
(item ! NULL) Post-condition item has
been added to c /
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void DeleteFromCollection( Collection c, void
item ) / Delete an item from a Collection
Pre-condition (c is a Collection created by a
call to ConsCollection)
(existing item count gt 1)
(item ! NULL) Post-condition item
has been deleted from c / void
FindInCollection( Collection c, void key ) /
Find an item in a Collection Pre-condition c
is a Collection created by a call to
ConsCollection key !
NULL Post-condition returns an item
identified by key if one
exists, otherwise returns NULL /
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More formal pre- and post-conditions

• No duplicates items with same key cannot be
  added to the collection

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/ Specification of a collection which contains
unique items only Assumes that the items of
which the collection is composed supply an
ItemKey method which returns the pointer to an
identifying key for the item / typedef struct
u_collection_struct u_collection u_collection
ConsUCollection( int max_items ) / Construct a
new collection Pre-condition None
Post-condition returns a pointer to an empty
collection / void AddToUCollection( u_collection
c, void item ) / Add an item to a collection
Pre-condition (c was created by a call
to ConsUCollection) (item ! NULL)
(FindInUCollection(c, ItemKey(item))NULL)
Post-condition FindInUCollection(c,
ItemKey(item)) ! NULL /
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void DeleteFromUCollection( u_collection c, void
item ) / Delete an item from a collection
Pre-condition (c was created by a call
to ConsUCollection) (item ! NULL)
(FindInUCollection(c, ItemKey(item)) !
NULL) Post-condition
FindInUCollection(c, ItemKey(item))
NULL / void FindInUCollection( u_collection c,
void key ) / Find an item in a collection
Pre-condition c is a collection created by a
call to ConsCollection
key ! NULL Post-condition
returns an item identified by key if
one exists, otherwise returns NULL /
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C conventions

• .h file
• Specifications which a user or client of the
  object needs to see are normally placed in this
  file with .h suffix to its name
• For the collection, we would place the specs in
  files called collection.h and Ucollection.h
• Use Cs include facility to import them into
  programs which needed to use them.
• .c file
• The implementation or body of the class is placed
  in a file with a .c suffix

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Error Handling

• Unexpected program failures are a disaster
• If an error is fatal ? i.e., if the program
  cannot sensibly continue, then the program must
  be able to die gracefully
• Inform its user why it died, and
• Save as much of the program state as possible
• What is an error?
• Careful specification of each software component
  is a requirement
• Pre-conditions of a method will specify the
  states of a system which a method is able to
  process ? specify all the acceptable input states
• Post-conditions of a method specify the result of
  processing each acceptable input
• ? Divide the responsibility of the errors

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Processing Errors
Error to be processed by the constructor for a
dynamically allocated object
X ConsX( .... ) X x malloc(
sizeof(struct t_X) ) if ( x NULL )
printf("Insuff mem\n") exit( 1 )
else .....
What is the problem?
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Processing Errors..

• Error message is cryptic
• Little help in locating the cause of the error
• At least be Insuff Mem for X
• Program will simply exit
• possibly leaving the system in some unstable,
  partially updated state
• What if the code is built into elaborate GUI
  program with no provision for standard output?
• We may have used the code in embedded processor
  with no way to process an output stream of
  characters
• Use of exit assumes the presence of higher level
  program such as Unix shell to process the error
  code
• General rule I/O is non-portable!
• Functions like printf will produce error messages
  on terminal, but where will the messages go if
  running a GUI program like Netscape

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C

• Programming Basics
• Input and Output
• Structures (Arrays, Pointers, Self-references,
  Table lookup, typedef, Unions, bit fields etc)
• Pointers and arrays
• Functions and program structure
• Control flow (if-else, loops, break, switch,
  continue, goto etc)
• Types, operators, and expressions

Challengers Call by value? External
variables? Conditional expression Recursion Initia
lization Pointers to functions Command-line
arguments Register variables Error handling
stderr Formats Scanf
Functions as a data type?
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C

• Know what is Unix and what is ANSI C
• Libraries
• ltstdio.hgt, ltstring.hgt, ltmath.hgt, ltstdlib.hgt,
  ltassert.hgt, ltsignal.hgt,lttime.hgt, ltctype.hgt
• Programming- Subtleties
• Conversions
• Expressions
• Declarations
• Scope
• Preprocessing

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C

• Dynamic memory allocation
• Operator new, delete
• Classes
• Operator overloading
• Exception handling
• Friends and protected Class members
• ifndef, define, and endif statements

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Debugging

• Test run produces a result different from the one
  expected
• Some thing wrong with the program
• Determine the cause and correct the discrepancy ?
  Debugging
• How to design test data?
• HOW TO DEBUG
• Logical reasoning
• Program trace
• Isolate the suspect and trace this part
• Debugger

Dos and donts Do not correct errors by creating
exceptions Correcting an error should not create
other errors Incremental testing and debugging To
test multi function program, begin testing
single function that is independent Introduce
other functions one at a time
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SW Guidelines

• Coding Style
• Header files, Comments
• Naming variables
• Indentation
• Compilation
• Makefile
• Execution
• Environment, shell, path
• Debugger
• Submission

Refer to the Guidelines for Programming
Homeworks document available on the course web
page
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Next Time

• Computational Complexity Program Performance
• Cormen Chapter 1, 2, 3, 4.1-4.3
• Terminology from Chapters 5 6
• Student TalkWho?
• To be announced
• TA and Demo Lab