Section 0: Introduction.

The Unconventional Desk Calculator, or udc as it shall henceforth be known, is
a conventional desk calculator in that it allows the assignment and
interrogation of mathematical expressions but it has additional features.
These include function definitions, normal and array structured variables,
logical operators such as 'and' and ‘or’, the if~then-else clause for use
inside arithmetic expressions and a range of explanatory error messages. This
particular version of the udc has been written in Berkeley Pascal. Because of
this the udc's implementation has been complicated by the restricted set of
software tools available. Software tools available in a comparable high level
language like C, for instance, mean that lexical analysers and parsers can be
written with greater ease.

This document has been designed to give an in depth explanation of the use and
abilities of the udc ( Section l ), to give an explanation of the workings and
algorithms involved in the actual program at the same time as explaining what
these processes are for and why they are necessary ( Section 2 ), to discuss
the novel features, restrictions, and problems incurred in this particular
implementation of udc ( Section 3 ), and finally to give Backus Normal form
specifications of udc programs and pseudo-code ( a translation from the high
level language to a not so detailed but easier to read, nearer to English
language ) for all procedures within the program ( Section 4 ).