Programming Languages

1
Programming Languages

• CPS120 Introduction to Computer Science
• Lecture 5

2
Programming Languages

• A programming language is a set of rules that
  provides a way of telling a computer what
  operations to perform.

3
Levels of Programming Languages

• Machine language
• Assembly Language
• High Level Languages
• Fourth Generation Languages (4GL)

4
Machine Languages

• different for each computer processor
• 0100
• 001101 100000 001101 110001
• 00101 10001 10000
• 01110
• 111001
• . . .

5
Assembly Languages

• different for each computer processor
• main proc pay
• mov ax, dseg
• mov ax, 0b00h
• add ax, dx
• mov a1, b1
• mul b1, ax
• mov b1, 04h

6
High-Level Languages

• Higher Level Languages
• Use traditional programming logic where the
  programming instructions tell the computer what
  to do and how to perform the required operations.
• 4GLs
• Use high-level English-like instructions to
  specify what to do, not how to do it .

7
Interpreter vs. Compiler

• Interpreter
• Translates instructions to machine code
  line-by-line.
• Compiler
• Translates the entire program to machine code
  before running it.

8
Types of Programming Languages

• Machine language
• Procedure-oriented languages
• Object-oriented languages
• Event-driven languages

9
Early Language History

• FORTRAN (short for Formula Translator, developed
  in the 1950s by IBM
• In 1958, a language called ALGOL (Algorithm
  Language) was developed
• COBOL (Common Business Oriented Language) was
  created in 1960 to serve as the primary language
  for large-scale programs
• In 1964, the BASIC language (Beginners
  All-Purpose Symbolic Instruction Code) was first
  used
• In 1965, a language called PL/I was developed in
  hopes of being everything to everyone.
• PL/I proved to be too complex.
• In the late 1960s, Niklaus Wirth developed a
  teaching language called Pascal.

10
Later Language History

• Ada, which was developed in 1983, is large and
  complex.
• Smalltalk is graphical and object-oriented.
  Concepts developed with Smalltalk were important
  to the development and continued development of
  languages like C and Java
• The C language was derived from ALGOL.
• C is C with the addition of object-oriented
  concepts.

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Procedure-Oriented Languages

• FORTRAN
• COBOL
• Pascal
• C
• Ada

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OOED Languages

• Object-oriented languages
• Smalltalk
• C
• Ada 95
• Event-driven languages
• Visual Basic
• most Visual languages

13
What Can a Program Do?

• A program can only instruct a computer to
• Read Input
• Sequence
• Calculate
• Store data
• Compare and branch
• Iterate or Loop
• Write Output

14
Fundamental Programming Concepts

• Assignment of values to a variable
• Iteration (Looping)
• Over a set of set of statements
• With respect to a logical expressions
  (conditions)
• Delegation of sub-tasks to functions / procedures

15
The Structure Theorem

• The Structure Theorem states that any algorithm
  can be built from three basic control structures.
  
• One-after-another (Sequence)
• Decision-making (Selection)
• Making choices between 2 or more alternatives
• Repetition (Iteration)
• Concerned with repetitive tasks (and the
  termination conditions of loops)

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C Control Structures

• "Sequence statements" are imperatives
• "Selection" is the "if then else" statement
• AND, OR, NOT and parentheses ( ) can be used for
  compound conditions
• "Iteration" is satisfied by a number of
  statements
• "while"
• " do "
• "for"
• The case-type statement is satisfied by the
  "switch" statement.
• CASE statements are used for most non-trivial
  selection decisions

17
Programmer Productivity Tools

• Modular Programming
• Structured Programming
• Object-oriented Programming

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Modular Programming

• Large programs are divided by functional parts
  into subroutines
• Strong cohesion
• Loose coupling

19
Structured Programming

• Composed of sequence, decision (selection), and
  repetition (looping or iteration) structures
• Structured program languages lend themselves to
  flowcharts, structure charts, and pseudocode.
• Structured programming languages work best where
  the instructions have been broken up into small,
  manageable parts.
• Looks at a problem as procedures
• Data are maintained separately from data

20
Structured Program Rules

1. Use only sequence, decision, and repetition
2. Only one entrance into and one exit from a
   structure
3. Connectors only allowed when continuing
   processing from one column or page to another
4. Decision and repetition structures can be nested
5. Only one STOP instruction is permitted. It must
   be in the MAINLINE routine

21
Structured Programming Advantages

• Standard method for solving problems
• GO-TO less
• Easier to test and debug
• Written by more than one programmer
• Reusability
• Thrashing minimized

22
Object-Oriented Programs

• Developed to respond to programming issues that
  structured programming did not adequately address
• Rarely possible to anticipate the design of a
  completed system before implementation
• GUIs were difficult to develop in traditional
  procedure-oriented languages
• Sharing data across routines is error prone
• Information hiding allows programmers to
  determine what data is exposed to various
  routines