Programming Concepts

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Programming Concepts

• David T. Makota
• Department of Computing Information Technology
  (CIT)
• The Institute of Finance Management
• Dar Es Salaam, Tanzania

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Contents

• Computer programs
• Programming
• Programmer
• Programming languages

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COMPUTER PROGRAMS

• A computer program is one or more instructions
  that are intended for execution by a computer.
• Computer programs may result from the compilation
  or interpretation of programming languages,
  direct result of hardware processing, or manually
  input to the central processor of a computer.
• A computer program does nothing unless its
  instructions are executed by a central processor.

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Computer programs cont

• A computer program expressed in a human-readable
  computer programming language is source code.
• Source code may be converted into an executable
  image by a compiler, or executed immediately with
  the aid of an interpreter.
• Compiled computer programs are commonly referred
  to as executables, binary images, or simply as
  binaries a reference to the binary file format
  commonly used to store the executable code.

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Computer programs cont

• Computer programs are generally specified using
  declarative, imperative, or visual programming
  methods.
• With the imperative approach, an algorithm is
  specified
• with the declarative approach, the output is
  specified and the implementation details are
  hidden.
• With a visual approach, program elements are
  graphically manipulated rather than specified
  textually.

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Computer programs cont

• Computer programs may be categorized along
  functional lines. These functional categories
  include application software, operating systems,
  video games, and compilers, among others.
• Computer programs embedded in hardware devices
  are called firmware.

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Computer programs cont

• Program execution
• Typically, computer programs are stored in
  non-volatile memory until requested either
  directly or indirectly by the computer user to be
  executed.
• Upon such a request the program is loaded into
  random access memory where it can be accessed
  directly by the central processor.
• The central processor then executes ("runs") the
  program, instruction by instruction, until
  termination, either by a successful
  self-termination or by either a software or
  hardware error.
• Modern day multiprocessor computers or computers
  with multicore processors may run multiple
  programs on a single computer simultaneously.

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Computer programs cont

• Computer programs can be divided into two
  categories
• Application software
• is a subclass of computer software that employs
  the capabilities of a computer directly and
  thoroughly to a task that the user wishes to
  perform.
• System software
• is a generic term referring to any computer
  software which manages and controls the hardware
  so that application software can perform a task.

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Computer programs cont

• Two Views of a Program

software layers hidden by user interface
user interface
users view
programmers view
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Computer programs cont

• Real world examples
• library catalogue
• word processor
• video game
• ATM

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PROGRAMMING

• Computer programming is the iterative process of
  writing or editing source code of computer
  programs, followed by testing, analyzing and
  refining this code.
• MANY ASPECTS OF PROGRAMMING
• Programming is controlling
• computer does exactly what you tell it to
• Programming is teaching
• computer can only learn to do new things if you
  tell it how
• Programming is problem solving
• always trying to make computer do something
  useful eg finding an optimal travel route

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Programming cont

• Many aspects of programming cont
• Programming is creative
• must find a good solution out of many
  possibilities
• Programming is modelling
• describe salient (relevant) properties and
  behaviours of a system of components (objects)
• Programming is abstraction
• identify important features without getting lost
  in detail
• Programming is concrete
• must provide detailed instructions to complete
  task

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PROGRAMMER

• A programmer or software developer is someone who
  programs computers, that is, one who writes
  computer software.
• The term computer programmer can refer to a
  specialist in one area of computer programming or
  to a generalist who writes code for many kinds of
  software.
• One who practices or professes a formal approach
  to programming may also be known as a programmer
  analyst, software engineer, computer scientist,
  or software analyst.

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Programmer cont

• Application versus system programming
• Computer programmers often are grouped into two
  broad types applications programmers and systems
  programmers
• Applications programmers write programs to handle
  a specific job, such as a program to track
  inventory within an organization.
• Systems programmers, in contrast, write programs
  to maintain and control computer systems
  software, such as operating systems and database
  management systems.

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PROGRAMMING LANGUAGES

• A programming language is an artificial language
  that can be used to control the behavior of a
  machine, particularly a computer.
• Programming languages, like natural languages,
  are defined by syntactic and semantic rules which
  describe their structure and meaning
• syntax grammatical rules for forming
  instructions
• semantics meaning/interpretation of instructions

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Programming languages cont

• programming languages allow you to
  expressyourself more precisely than natural
  language
• as a result, programs cannot be ambiguous

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Programming languages cont

• Categories of programming languages
• Machine language
• machine is short for computing machine (i.e.,
  computer)
• computers native language
• sequence of zeroes and ones (binary)
• different computers understand different
  sequences
• hard for humans to understand
• 01010001...

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Programming languages cont

• Categories of programming languages
• Assembly language
• mnemonics for machine language
• low level each instruction is minimal
• still hard for humans to understand
• ADD.L d0,d2

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Programming languages cont

• Categories of programming languages
• High-level languages
• FORTRAN, Pascal, BASIC, C, C, Java, etc.
• high level each instruction composed of many
  low-level instructions
• closer to English and algebra
• easier to read and understand

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Software Development A 5-Step Process
The Waterfall Model
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Software Development cont

• Analysis
• English description of system models, to meet a
  requirement or specification
• work with potential users to develop detailed
  specifications
• May be written by non-programmer

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Software Development cont

• Designing the system
• divide conquer system is composed of smaller
  subsystems which in turn may be composed of even
  smaller subsystems
• pseudocode somewhere between English and program
  code
• describe tasks, subtasks, and how they relate
• hand-simulation desk-check pseudocode by
  stepping through it without using a computer
• often use diagrams to better communicate the
  structure of the system

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Software Development cont

• Implementing the design
• emphasis on good problem decomposition, well
  structured design, and readable, well-documented
  programming style
• hand-simulate as you go, may need to backtrack
  and redesign
• if design is good, most of the hard work should
  be done

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Software Development cont

• 4) Testing and Debugging
• testing submitting input data or sample user
  interactions and seeing if program reacts
  properly
• typically done in stages, starting with
  individual components and working up to
  subsystems, and eventually the entire program
• debugging process of removing program bugs
• bugs errors in code or design

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Software Development cont

• 5) Maintenance
• finally, keep the program working and current
• in a successful piece of software, maintenance is
  often said to be 80 of the effort
• Result Working program
• solves original problem

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Software Development cont

• Good program
• satisfies the specification
• produced on time and within budget
• user-centric design
• uses creativity to solve problem
• well structured/organized/written/documented
• can be easily extended and maintained