CS101 - Introduction to Computing - Lecture Handout 19

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Programming Languages

During the last lecture …

We continued our discussion on algorithms that we had started during the 16th 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
Last time we discussed what to implement
Today’s Lecture
Today we are going to discuss the tool that is used to implement SW
To understand the differences among low- & high-level, interpreted & compiled, and structured & object-oriented programming languages
To understand the role of programming languages in computing


The process of telling the computer what to do


Batch Programs
Event-Driven Programs

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

Programming Language

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

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

Programming Language

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

All programs consists of:

Sequence of instructions

These may contain:

Input/output (print, etc)
Operations (add, divide, etc)

Examples of Prog. Languages


Types of Prog. Languages

High level Programming Languages
Low Level Programming Languages
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 microprocessors has its own unique machine language lying between machine languages & high-level languages are languages called Assembly languages
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.

Languages 1

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
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
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
The choice of which language to use can also depend on the:

  • Type of computer the program is to run on,
  • Expertise of the programmer

Interpreters: immediate response, but execute code slowly.
Compilers: Takes longer to compile, but super-fast execution.
Both interpreters and compilers are available for most high-level languages.
However, BASIC and LISP were especially designed to be executed by an interpreter.
Why are there so many different programming languages?
What are the advantages of particular languages?
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

  • Can a single language have all the good bits of other languages?
  • Is there a perfect language?
  • Do some good features force a language to also have bad features?
  • What makes a feature good or bad?
  • What makes a feature good or bad?

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
What changes in the field of computer languages can we expect in the near future?
-Which programming language should you learn?
Should you learn more than one?

Programming SW Development

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

Object Oriented Design

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
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

Structured Design

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 redesign exercise
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

Object-Oriented Languages

Programming languages specifically designed to make it easy to implement objectoriented designs
Examples: Smalltalk, C++, Java

Programming Languages


What is Object-Oriented Software?

VisualBasic: Taming the Wooly Mammoth
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

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