COMPUTER PROGRAMS AND LANGUAGES Chapter 4

Developing a computer program Programs 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-

Flowcharts A 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 addition 4 x

Even/Odd number

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

Computer languages Natural 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 11add contents of location 11 to accumulator ADD 12add contents of location 12 to accumulator STA 13copy contents of accumulator into a location 13 STPstop - no more instructions Assembler?

Evolution … Third Generation High level, general-purpose FORTRAN, LISP, COBOL, ALGOL Ada, Basic, C, C++, Java, Pascal, Smalltalk Easier for humans to read, write, debug Compiler translates into machine code before running Interpreter 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

Assignments IOA, 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/1 Algol 60 Algol 68 Pascal Modula 3 Ada C C++ Simula Smalltalk Java Dylan Ruby Perl Python C#

BASIC (1964) Developed at Dartmouth in 1960’s by Tom Kurtz, John Kemeny, and a succession of undergraduates; first ran in 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