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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