1 CS101 Introduction to Computing Lecture 19 Programming Languages

2 During the last lecture … We continued our discussion on algorithms that we had started during the 16 th lecture In particular, we looked at the building blocks that are used in all algorithms We also discussed the pseudo code and flowcharts for particular problems In addition, we outlined the pros and cons of those two techniques

3 Last time we discussed what to implement Today we are going to discuss the tool that is used to implement SW

4 Today’s Lecture To understand the role of programming languages in computing To understand the differences among low- & high-level, interpreted & compiled, and structured & object-oriented programming languages

5 Programming ?

6 The process of telling the computer what to do Also known as coding

7 Types of Programs ?

8 Batch Programs These are typically started from a shell (or automatically via a scheduler) and tend to follow a pattern of: –Initialize internal data –Read input data –Process that data –Print or store results Key feature: No user interaction with the computer while the program is running Examples?

9 Event-Driven Programs Examples? GUIs, microwave, camera The system sends events to the program and the program responds to these as they arrive. Events can include things a user does - like clicking the mouse - or things that the system itself does - like updating the clock. These programs generally work as follows: –Initialize the internal data –Wait for events to arrive –Identify an incoming event and react accordingly

10 Programming Language ?

11 A vocabulary and set of grammatical rules for instructing a computer to perform specific tasks

12 All programs consists of: 1.Sequence of instructions 2.Conditionals 3.Loops These may contain: –Data –Input/output (print, etc) –Operations (add, divide, etc)

13 Examples of Programming Language ?

14 Machine Language Assembly Language ( ) LISP (1956) Fortran (1957) COBOL (1959) PL/1(1964) BASIC (1964) Pascal (1970) Smalltalk (1972) C (1972) Ada(1983) C++ ( ) QBasic (1986) Perl (1987) VisualBasic (1991) PowerBuilder Java (1995) JavaScript C# (2001)

15 Is HTML a programming language ?

16 Types of Programming Languages ?

17 High level Programming Languages Low Level Programming Languages

18 High-level programming languages, while simple compared to human languages, are more complex than the languages the uP actually understands, called machine languages Each different type of uP has its own unique machine language

19 Lying between machine languages & high-level languages are languages called assembly languages

20 Assembly languages are similar to machine languages, but are easier to program in as they allow a programmer to substitute names for numbers Machine languages consist of numbers only

21 4th-generation languages High-level languages Assembly languages Machine languages

22 walks!

23 Regardless of what language you use, you eventually need to convert your program into a language that the computer can understand Two ways for doing that: compile the program or interpret the program

24 Interpreter is a program that executes instructions written in a high- level language An interpreter translates high-level instructions into an intermediate form, which it then executes In contrast, a compiler translates high-level instructions directly into machine language

25 Compiled programs generally run faster than interpreted programs The advantage of an interpreter, however, is that it does not need to go through the compilation stage during which the whole of the high-level code is translated into machine instructions in one go. This process can be time-consuming if the program is long. The interpreter can immediately execute high- level programs, without waiting for the completion of the translation process

26 Interpreters: Immediate response, but execute code slowly Compilers: Takes longer to compile, but super-fast execution

27 Both interpreters and compilers are available for most high-level languages. However, BASIC and LISP were especially designed to be executed by an interpreter

28 Why are there so many different programming languages ?

29 What is the difference between them ?

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31 What are the advantages of particular languages ?

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33 The question of which language is best is one that consumes a lot of time and energy among computer professionals Every language has its strengths and weaknesses

34 FORTRAN is a particularly good language for processing numerical data, but it does not lend itself very well to large business programs Pascal is very good for writing well-structured and readable programs, but it is not as flexible as the C programming language C++ embodies powerful object-oriented features, but it is complex and difficult to learn

35 The choice of which language to use can also depend on the: type of computer the program is to run on, and the expertise of the programmer

36 Can a single language have all the good bits of other languages ?

37 Do some good features force a language to also have bad features ?

38 What makes a feature good or bad ?

39 Is there a perfect language ?

40 Is there a perfect language for a particular task ?

41 What changes in the field of computer languages can we expect in the near future ?

42 Which programming language should you learn ? Should you learn more than one ?

43 ? Programming SW Development

44 Design SW Design Methodology ?

45 The set of (often flexible) rules and guidelines a team of developers follow to construct reasonably complex SW systems

46 Object Oriented Design (1) OO SW is all about objects: a black box which receives messages & responds with those of its own An object has 2 aspects: –State, also termed as properties, data Example: For the bicycle: color, speed, pressure –Behaviors, also termed as methods, instructions Example: For the same object: accelerate(), inflate() In traditional design, these 2 aspects have been kept apart

47 Object Oriented Design (2) The designer starts with any component (object) of the system; designs it as an independent, self-contained system, and then moves to the design of some other component The over-all system is put together by fitting together a collection of these components Key feature: Details of the design of the component are kept independent of the over-all system –Benefit: It can be easily re-used in other systems: design once; use multiple times

48 Structured Design (1) Also called top-down design The designer starts by first conceiving a skeleton high-level design of the system, and then starts defining features of that over-all design in an ever-increasing detail Making small changes in the functionality of the systems sometimes leads to major re-design exercise

49 Structured Design (2) Structured design emphasizes separating a program's data from its functionality Separating data from functionality typically leads to SW that is difficult to maintain & understand - especially for large SW systems

50 Object-Oriented Languages Programming languages specifically designed to make it easy to implement object-oriented designs Examples: Smalltalk, C++, Java

51 Reading Material Programming Languages What is Object-Oriented Software? VisualBasic: Taming the Wooly Mammoth

52 During Today’s Lecture, We … To understand the role of programming languages in computing To understand the differences among low- & high-level, interpreted & compiled, and structured & object-oriented programming languages

53 Focus of the Next Lecture: The SW Development Process Development process of reasonably complex SW systems does not consist of “coding” only We will become familiar with the various phases of the process that developers follow to develop SW systems of reasonable complexity