Department of Computer and Information Science, School of Science, IUPUI

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Department of Computer and Information
Science,School of Science, IUPUI
CSCI 230
Introduction to Computers - Languages
Dale Roberts, Lecturer Computer Science,
IUPUI E-mail droberts_at_cs.iupui.edu
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Computer Organization

• A Typical Von-Neumann Architecture
• Example
• Input unit
• Output unit
• Memory unit
• Arithmetic and logic unit (ALU)
• Central processing unit (CPU)
• Secondary storage unit

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Programming Languages

• Machine languages (machine dependent)
• Native tongue of a particular kind of computer.
  Each instruction is a binary string. The code is
  used to indicate the operations to be performed
  and the memory cells to be addressed. This form
  is easiest form of computers to understand, but
  is most difficult for a person to understand.
• Strings of numbers giving machine specific
  instructions
• Example 1300042774
• 1400593419
• 1200274027

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Programming Languages (cont.)

• Assembly languages (machine dependent)
• English-like abbreviations representing
  elementary computer operations (translated via
  assemblers)
• Again specific to only one type of computer. Uses
  descriptive names for operations and data, e.g. ,
  LOAD value, ADD delta, STORE value.
  Assemblers will translate these to machine
  languages. Intermediate level. Somewhat
  descriptive, but basically following the machine
  instructions.
• Example LOAD BASEPAY
• ADD OVERPAY
• STORE GROSSPAY

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Programming Languages (cont.)

• High-level languages (machine independent)
• Codes similar to everyday English
• High-level languages Write program instructions
  called statement that resemble a limited version
  of English. e.g., the statement value value
  delta. Portable, meaning it can be used on
  different types of computers without
  modifications. Compilers translate them to
  machine languages. Examples are FORTRAN, PASCAL,
  COBOL, C, C, BASIC etc.
• Use mathematical notations (translated via
  compilers)
• Example
• grossPay basePay overTimePay
• Example
• Statement a a b

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Programming Languages (cont.)

• Structured programming
• Disciplined approach to writing programs
• Clear, easy to test and debug and easy to modify
• Multitasking
• Specifying that many
• activities run in parallel (still timesliced)

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Semantic Gap

• A semantic gap exists between the amount of
  information conveyed in assembly language v high
  level languages. Consider the following C single
  statement x x 3
• This single statement may require many assembly
  language statements (operations) Load memory
  location 24 into accumulator Add a constant 3
  to the accumulator Store accumulator in
  memory location 24
• The number of executable statement expands
  greatly during the translation process from a
  high level language into assembly language.

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C Programming Language

• C
• High-level general-purpose language developed in
  1972 at ATT Bell Lab. By Dennis Ritchie from two
  previous programming BCPL and B
• Originally developed to write the UNIX operating
  system
• Hardware independent (portable)
• By late 1970's C had evolved to "Traditional C"
• Today, virtually all new operating systems are
  written in C or C.
• The current standard in C is ANSI C.
• C is a more advanced version of C,
  incorporating among other things, the
  object-oriented constructs
• Standardization
• Many slight variations of C existed, and were
  incompatible
• Committee formed to create a "unambiguous,
  machine-independent" definition
• Standard created in 1989, updated in 1999
• C has become a popular language industry due its
  power and flexibility

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The C Standard Library

• C programs consist of pieces/modules called
  functions
• A programmer can create his own functions
• Advantage the programmer knows exactly how it
  works
• Disadvantage time consuming
• Programmers will often use the C library
  functions
• Use these as building blocks
• Avoid re-inventing the wheel
• If a pre-made function exists, generally best to
  use it rather than write your own
• Library functions carefully written, efficient,
  and portable

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The C Standard Library (cont.)

• The Key Software Trend Objects in C and JAVA
• Reusable software components that model items in
  the real world
• Meaningful software units ex Date objects, time
  objects, audio objects, video objects, file
  objects, record objectsany noun can be
  represented as an object
• More understandable, better organized, and easier
  to maintain than procedural programming
• Favor modularity

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The C Standard Library

• include ltstdio.hgt
• main()
• int i
• for (i 0 i i lt 10)
• printf ("Hello World!\n")

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A Typical C Program Development Environment

• 1. Edit
• 2. Preprocess
• 3. Compile
• 4. Link
• 5. Load
• 6. Execute

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A Typical C Program Development Environment
(cont.)

• Procedure to Prepare a C Program for Execution

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Constructs in C Language

• Type Declarations ex int, float,
• I/O ex printf(), scanf()
• Arithmetic and Logical Operations ex
  ,-,,/,,gt,lt,,
• Arrays, Pointers, Structures, Unions,
• Functions
• Arguments return values
• Recursion
• Control Mechanisms ex if, else, while, for,
• Characters Strings ex strcat(), strcpy(),
• File Processing ex fopen(), fclose(),
• Pre-processor ex define
• Misc.
• bit operations, ...

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Operation System (OS)

• Responsibilities
• Communicating with the computer user
• Managing allocation of memory, of processor
• time, and of other resources for various tasks
• I/O handling BIOS vs DOS services (Interrupts)
• Read/Write data from secondary storage
• Evolution of Operating Systems
• Batch processing do only one job or task at a
  time
• Operating systems manage transitions between
  jobs and Increase throughput (amount of work
  computers process)
• Multiprogramming Computer resources are shared
  by many jobs or tasks
• Timesharing Technique used to implement
  multiprogramming where the computer runs a small
  portion of one users job then moves on to
  service the next user

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Application Software

• Developed to assist a computer user in
  accomplishing special tasks
• ex word processing applications MS-word or
  Word-perfect
• ex Spreadsheet applications Lotus1-2-3, Excel
• ex Database Oracle, MS-Access
• Software Development Life Cycle (SDLC)
• Problem specify the problem requirements
• Analysis analyze the problem
• Design design the algorithm to solve the problem
• Implementation Implement the algorithm
• Testing test and verify the completed program
• Maintenance maintain and update the program