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High level Languages

Very early in the development of computers attempts were made to make programming easier by reducing the amount of knowledge of the internal workings of the computer that was needed to write programs. If programs could be presented in a language that was more familiar to the person solving the problem, then fewer mistakes would be made. High-level programming languages allow the specification of a problem solution in terms closer to those used by human beings. These languages were designed to make programming far easier, less error-prone and to remove the programmer from having to know the details of the internal structure of a particular computer. These high-level languages were much closer to human language. One of the first of these languages was Fortran II which was introduced in about 1958. In Fortran II our program above would be written as:

C = A + B
which is obviously much more readable, quicker to write and less error-prone. As with assembly languages the computer does not understand these high-level languages directly and hence they have to be processed by passing them through a program called a compiler which translates them into internal machine language before they can be executed.

Another advantage accrues from the use of high-level languages if the languages are standardised by some international body. Then each manufacturer produces a compiler to compile programs that conform to the standard into their own internal machine language. Then it should be easy to take a program which conforms to the standard and implement it on many different computers merely by re-compiling it on the appropriate computer. This great advantage of portability of programs has been achieved for several high-level languages and it is now possible to move programs from one computer to another without too much difficulty. Unfortunately many compiler writers add new features of their own which means that if a programmer uses these features then their program becomes non-portable. It is well worth becoming familiar with the standard and writing programs which obey it, so that your programs are more likely to be portable.

As with assembly language human time is saved at the expense of the compilation time required to translate the program to internal machine language. The compilation time used in the computer is trivial compared with the human time saved, typically seconds as compared with weeks.

Many high level languages have appeared since Fortran II (and many have also disappeared!), among the most widely used have been:
COBOL Business applications
FORTRAN Engineering & Scientific Applications
PASCAL General use and as a teaching tool
C & C++ General Purpose - currently most popular
PROLOG Artificial Intelligence
JAVA General Purpose - gaining popularity rapidly
All these languages are available on a large variety of computers.


next up previous
Next: Summary Up: Programming Languages Previous: Assembly Language
Peter JB King
1999-08-31