computer programs and languages

COMPUTER PROGRAMS AND LANGUAGES

Chapter 4

Developing a computer programPrograms are a set (series) of instructions

Programmers determine• The instructions to be performed.• The order in which those instructions

are to be performed.• The data required to perform those

instructions.

Program Development- Where to start?

Algorithms The most basic tools that are used to

develop the problem-solving logic• steps are unambiguous • a finite number of steps

• that repeat (iterate) • require decisions (logic and comparison) until

the task is completed

Different algorithms may accomplish the same task, with a different set of instructions, in more or less the same time, space, and efforts.

Example-

FlowchartsA pictorial representation of an algorithm • steps in the form of different shapes of

boxes • logical flow (sequence) by

interconnecting arrows• help the programmer in understanding

the logic of the program• Flowcharts outline the general

procedure

• Comparable to blueprint of a building• draws a flowchart prior to writing a program• standard flowchart symbols prescribed by

the American National Standard Institute (ANSI).

Multiplication by addition4 x 200

200200200200

Even/Odd number

Calculate factorial- 5! = 5*4*3*2*1

Computer languagesNatural languages are ambiguous, vaguely

structured (vs. well defined), and has very large and ever changing (vs. well defined and a stable set) vocabularies

• Machine language (Low level )• Difficult to understand

• Assembly language (Low level )• Symbolic instructions of executable machine

codes• High level language

• Some rules similar to spoken

Evolution• Programming languages have evolved

tremendously• hundreds of different languages• user-friendly and more powerful• five generations

First Generation: Machine/Native Language

• Binary- every instruction and data using 0/1

• Instruction consists of two parts • Operation & Operand- where to find or store

the data (operation)• Fast and efficient, executed directly on the

CPU• Difficult for humans to read, write, and

debug

Evolution …Second generation- Assembly Language• Programs can be written symbolically, using

English words (also known as mnemonics)

LDA 10 copy the contents of location 10 into the accumulator

ADD 11 add contents of location 11 to accumulator ADD 12 add contents of location 12 to accumulator STA 13 copy contents of accumulator into a location 13 STP stop - no more instructions Assemble

r?

Evolution …Third Generation• High level, general-purpose• FORTRAN, LISP, COBOL, ALGOL• Ada, Basic, C, C++, Java, Pascal, Smalltalk

Easier for humans to read, write, debugCompiler translates into machine code before

runningInterpreter translates into machine code at

runtime

Evolution …Fourth Generation• Specification languages, query languages,

report generators, application generators• Maple, Mathematica, Postscript, SPSS, SQL

Fifth Generation• Solve problems using constraints rather than

algorithms, used in Artificial Intelligence• Prolog

AssignmentsIOA, IA, GA, Case !@#$

A = 10, B = 20, K = 5, and SALES = 10000

A family tree of languages

Fortran

BASIC

Cobol LISP

Scheme

ML

Prolog

PL/1Algol 60

Algol 68Pascal

Modula 3Ada

C

C++

Simula

Smalltalk

Java

Dylan

Ruby

Perl

PythonC#

BASIC (1964)• Developed at Dartmouth in 1960’s by Tom Kurtz, John Kemeny,

and a succession of undergraduates; first ran in 1964.• Beginner’s All-purpose Symbolic Instructional Code• Intended to introduce students in non-scientific disciplines to

computing.• Influenced by FORTRAN and ALGOL.• Major goal to simplify user interface:

• Simplicity chosen over efficiency• Time sharing over punched cards• Distinctions such as int vs real eliminated• Automatic defaults for declarations, values, arrays, output format,

etc.• Clear error messages• Students had access to computers at all times

• No universal BASIC standard: • ANSI (American National Standards Institute) is a minimal standard.• True Basic – Kemeny’s company