Programming for A2 Computing

High Level Languages

By David Halliday

Module 4

High and Low Level languages• High Level languages• Examples:

– C, C++

– Pascal

– BASIC

• Portable (can be compiled on different systems)

• Problem oriented (designed around solving different types of problem)

• Statements resemble English language (formalised)

• Low level Languages• Examples

– Assembly

• Machine Oriented: designed for individual machine or processor architectures

• Each statement translates into one machine instruction

• Statements resemble machine instructions in mnemonics

High Level Language Facilities

• Selection statements:– If, Then, Else, Case

• Iteration (repetition) statements:– While...EndWhile, Repeat...Until, For… EndFor

• Built in/Library routines, functions and enumerated data types to simplify I/O– Readln, writeln– Sqr, log– String, Array, Record

High Level Language Paradigms• High level languages often fit into one of 3 categories

– Imperative (procedural)• Imperative programs explicitly specify an algorithm to achieve a goal• Examples include:

– C, C++– Pascal– Fortran

– Declarative• Declarative programs explicitly specify the goal and leave the

implementation of the algorithm to the support software • Examples include:

– Prolog

– Functional• Emphasizes the application of functions, unlike imperative programming,

which emphasizes changes in state and the execution of sequential commands.

• Examples include:– Haskell

Imperative (procedural) Languages• Imperative programs explicitly specify an algorithm to achieve a goal• They are concerned with changing of states of variables in memory• The closest paradigm to assembly/machine code• Problem Oriented… They are developed to solve particular types of

problem:– FORTRAN (FORmula TRANslation)

• dev'd in 1950s for use in scientific and engineering

– COBOL (COmmon Business Oriented Language)• dev'd in 1950s for data processing (first to use records)

– 'C‘• developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories for

use with the Unix operating system.

– Pascal• dev'd in 1970s to teach structured programming• Extended by Boreland with Delphi making a useful RAD tool

Embedded systems

• Computer is component in a larger system.• Examples include:

– microprocessor-controlled washing machine or video recorder;– a modern jet aircraft;– a system for controlling traffic lights;– a process control system for controlling the flow of water along a

pipe by means of a valve;– a robot used in a car assembly plant.– Modern mobile phones

Criteria for Selecting a Language

• The nature of the application;• The availability of facilities within the language for

implementing the software design;• The availability of a suitable compiler/interpreter for the

hardware; • The expertise of the programmers.

Homework

• Heathcote Chapter 35 Page 219 All Questions