Computer Languages: Empowering Algorithms

1
Computer Languages Empowering Algorithms

• How is it computers know what we want them to do?
• In this chapter
• What makes up a language and how do we use
  language to communicate with each other and with
  computers?
• How did computer programming languages evolve?
• How do computers recognize what we type in as
  programs?
• What do most programming languages have in
  common?
• What are the steps in building a program?

2
How does a person communicate with a computer?

• Communication cycle between humans.

Speaker encodes information
Listener decodes information
Listener returns feedback to speaker
3
How does a person communicate with a computer?

• Communication cycle between a human and a
  computer.

User encodes information
Computer decodes information
Computer returns results to user
4
How does a person communicate with a computer?

• Programming languages bridge the gap between
  human thought process and computer binary
  circuitry.

5
Are computer languages the same as human
languages?

• Similarities and differences between human
  (natural) and computer (programming) languages
• Semantics, Syntax, and Participants.
• Semantics
• Refers to the meaning.
• Human the concept a group of words represents.
• Computer the commands you wish the computer to
  perform.

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Are computer languages the same as human
languages?

• Syntax
• Refers to the grammatical structure of a
  language.
• Both human and computer sentence structure,
  spelling, and punctuation.
• Participants (Most obvious differences)
• Humans use human languages to communicate with
  each other.
• Humans use programming languages to communicate
  with computers.
• Computers only use binary code.

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A Programming Language Family Tree
Generation Class Description Examples Dates

1st Machine Binary representation of
operation ROBOT 1940s Generation Language codes
in 1s and 0s. Instruction Machine
specific Set 2nd Assembly Mnemonic
representation of Pencil Paper 1950s-60s Genera
tion Language operation codes Instruction
Set Machine specific 3rd High level
Code resembles English COBOL, 1960s Generation La
nguages language-like structure FORTRAN, to
present Transportable from one
machine BASIC, Pascal to another Ada 4th Non
- Query languages, PROLOG, QBE, 1980s-90s Gene
ration Procedural Application Generators, SQL,
Hypertalk Languages Report
Writers Smalltalk, QUEL 5th Natural
Incorporates spoken language, No common 1990s
to Generation Languages Relies on voice
recognition, and examples yet 21st speech
generation Century External appearance of
a human language
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A Programming Language Family Tree

• Parts of example programs

Machine Language 10000001 00001110 Load contents
of memory location num1 01100000 00001101 Add
the contents of memory location
num2 10100000 00001111 Store results into memory
location sum
High-level program sums(input,
output) language var num1, num2, sum
Integer begin read(num1, num2) sum
num1 num2 writeln(sum) end.
Assembly Read num1 Language Read num2 Load num1
Add num2 Store sum Print sum Stop
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A Programming Language Family Tree

• Comparative characteristics of computer language
  translators
• Assemblers, Interpreters, and Compilers.
• Assembled languages
• Assembler a program used to translate Assembly
  language programs.
• Produces one line of binary code per original
  program statement.

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A Programming Language Family Tree

• Interpreted languages
• Interpreter a program used to translate
  high-level programs.
• Translates one line of the program into binary
  code at a time.
• As each line is translated
• First, the Interpreter checks the one instruction
  for errors (source code).
• Next, it translates the instruction into binary
  code (object code).
• Last, it attempts to execute the binary coded
  instruction.
• The process repeats for the entire program.

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A Programming Language Family Tree

• Compiled languages
• Compiler a program used to translate high-level
  programs.
• Translates the entire program into binary code
  before anything is sent to the CPU for execution.
• The translation process for a compiled program
• First, the Compiler checks for errors in the
  entire program (source code).
• Next, it translates all of the instructions into
  binary code (object code).
• Last, the CPU attempts execution only after the
  programmer requests that the program be executed.

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Minimal Language Requirements The Bare Essentials

• Three generalized goals we humans wish for the
  computer to accomplish
• Organize data
• Calculate results
• Present results
• Five categories of computer language essentials
  if we are able to program computers to accomplish
  these three goals
• Program formatting, Data formatting, Data
  manipulation, Program Input/Output.

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Minimal Language Requirements The Bare Essentials

• Program formatting rules used to recognize
  tasks.
• Beginnings and endings of program units.
• Statement format rules including punctuation,
  capitalization, line numbering, and relationships
  to one another.
• Reserved words are terms used by the programming
  language for pre-defined purposes.
• Comments allow the programmer to provide
  information notations within a program.

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Minimal Language Requirements The Bare Essentials

• Data formatting rules used by the programming
  language to store information within the
  computers memory.
• Data types and Data structures.
• Data types identifying the type of a piece of
  information.
• Integer - Whole numbers
• Real - Numbers that contain fractional parts
• Character - Symbols
• Boolean - A way to store TRUE or FALSE

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Minimal Language Requirements The Bare Essentials

• Data Structures a way to connect data types
  together into more complex structures.
• Character string - stringing symbols together
  into words and sentences.
• Array - a list of data elements, all of the same
  type, which are stored one right after another in
  the computers memory, and which can be accessed
  by using just one memory-location name.
• Record - Groups together data items under one
  name that can be of different types and all
  pertain to one instance or individual.

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Minimal Language Requirements The Bare Essentials

• Representation examples of Data Structures

Character string This is a string of
characters! Array Friends list (contents of
array elements 1 - 3) 1) Sam 2) Lisa 3)
George Record Phone directory (contents of
records 1 2) 1) George Blass
2) Rick Marcus 14192 Ridgewood Dr. 29600
State Street South Lyon, MI 48178 Ypsilanti, MI
48197 248-555-1234 734-545-4321
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Minimal Language Requirements The Bare Essentials

• Data Manipulation
• Declaration statements (or data definition) -
  tells the computer which data types and
  structures will be used.
• Executable statements - series of instructions
  used to manipulate and transform various kinds of
  data.
• Control statements - series of statements that
  change the physical sequence order of instruction
  execution - Includes Conditional statements
  Iteration statements.

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Minimal Language Requirements The Bare Essentials

• Schematic representation of a simple conditional
  control statement

IF
True
False
Statement
Program Continues
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Minimal Language Requirements The Bare Essentials

• Schematic representation of a looping
  (repetition) programming structure

Count 0
Is Count Less Than 100?
Write Will not be late
Add 1 to Count
Done
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Minimal Language Requirements The Bare Essentials

• Program Input/Output
• Input - One or more statements instructing the
  computer to read the data from some appropriate
  device.
• Output - Needed in a program to tell the computer
  to send its program results to some appropriate
  output device.

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Building a Program

• Whatever type of problem needs to be solved, a
  careful thought out plan of attack, called an
  algorithm, is needed before a computer solution
  can be determined.
• 1) Understanding the problem.
• 2) Developing the algorithm.
• 3) Writing the program.
• 4) Testing and debugging.

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Building a Program

• 1) Understanding the problem.
• Need to analyze the problem and devise a plan for
  its solution
• Example What is needed to write a program that
  will print out the names of the students in your
  class?

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Building a Program

• 2) Developing the algorithm.
• Algorithm A detailed description of the exact
  methods used for solving a particular problem.
• Flow charts - series of visual symbols
  representing the logical flow of a program.
• Nassi-Schneidermann charts - uses specific shapes
  and symbols to represent different types of
  program statements.
• Pseudo code - a verbal shorthand method that
  closely resembles a programming language, but
  does not have to follow a rigid syntax structure.

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Building a Program

• Example of a flow chart method of describing an
  algorithm

Count 0
Is Count Less Than 100?
Write Will not be late
Add 1 to Count
Done
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Building a Program

• Example of a Nassi-Schneidermann chart for
  describing an algorithm

Start name-counter at zero False
name-counterlt30?
True Do Get a name from the keyboard Nothing Add
1 to the name-counter Print name-counter, name
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Building a Program

• Example of a Pseudo code solution of an algorithm

Start namecount 0 repeat until namecount
30 read name namecount namecount 1 print
namecount, name end repeat stop
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Building a Program

• After the program has been written
• 4) Testing and Debugging the Program.
• The program must be free of syntax errors.
• The program must be free of logic errors.
• The program must be reliable.
• (correctly produces correct results)
• The program must be robust.
• (able to detect execution errors)
• Alpha testing - within the company
• Beta testing - sophisticated users

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Real-World Programming Today

• Comparative sizes of real-life programs

Type of program Number of Lines The ROBOT
simulator Over 1000 lines The compiler for a
language with a limited instruction set Tens
of thousands of lines A full-featured word
processor Hundreds of thousands of lines A
microcomputer operating system Approximately
2,000,000 lines A military weapon management
program (controlling missiles, for
example) Several million lines
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Real-World Programming Today

• Comparing programs by time
• Commercial software is seldom written by
  individuals.
• Person-months - equivalent to one person working
  forty hours a week for four weeks.
• Person-years - equivalent to one person working
  for twelve months.
• Team of 5 working 40 hours for 8 weeks ten
  person-months.