Thursday, 29 January 2015

Pascal Programming Interview Questions and Answers

6. What are the major dialects of Pascal in use today?
There have been many implementations of Pascal, both those that follow and those that don't follow the ISO 7185 standard. For the most part, ISO 7185 was followed on large computer installations during the early days of Pascal (1973-1990), and some installations on microcomputers. The other dialect that became popular was the UCSD (University of California at San Diego) Pascal, followed by Borland's Turbo Pascal. Although there are virtually no current implementations of UCSD Pascal, Borland's products exist today for advanced IBM-PC compatibles under Borland's Delphi name.
When the IBM-PC became 32 bit with the introduction of the Intel 80386, virtually all of the 32 bit implementations of Pascal on the PC were ISO 7185 conforming. However, there was a large shakeout of compiler vendors in the early 1990's that removed many of these installations from the market.

7. What is IP Pascal?
A. IP is an interplatform Pascal. It supports the following platforms in its current configuration:
1. Windows/95/98/ME/NT/2000/XP.
2. Linux/86.
A port for Mac OS X is under way, and a port for Sun Solaris/Sparc is planned.
IP both provides, and itself is run, on a set of porting modules that allow IP, and its client programs, to run on any of the supported platforms without source change. To move within operating systems on the same machine type, only a relink is required. To move within different CPU based systems, a recompile and link is required.

8. Can IP Pascal compile my Turbo/think/MWP Program?
A few Turbo Pascal "units" that aid program porting have been created, and these have shown to dramatically simplify porting from that language. Similar procedures will be used for other Pascals. However, these are just rapid porting aids, and these Pascals do not enjoy full language compatibility. There will always be a minimum amount of work required to change programs to work under IP. Further, porting using these units won't give you a program that takes advantage of the features of IP, and I consider it to be only a step in the process of fully porting a program to IP.
IPs main focus is to be a language that is not tied to any operating system or hardware, and IP will, therefore, always be unable to fully emulate the machine dependent features of many Pascal implementations. The failure of many Pascals that are single machine based has shown that the future lies in very portable Pascal languages and compilers.

9. Why use the standard version of the language (when other dialects are more widely used)?
ISO 7185 standard is the original language as created by N. Wirth, more precisely defined and more secure than the original. The standard makers refrained from making large improvements or extensions to the language. In fact, because Pascal is one of the most carefully designed languages and also one of the most carefully standardized, there is a high degree of ability to determine, unambiguously, if a given program construct is legal according to ISO 7185 rules.
Pascal, almost from the first of its use, was widely extended and changed. One reason for this may be that the language was also very popular in compiler classes, and tended to produce many experimental versions.
The original language, Pascal/1972 or J&W Pascal, has been around since 1972, standardized in 1982, and only minor changes were required to programs to bring them into compliance with it (see below). The basis of the language is still very strong, and the ISO 7185 standard is freely available. Further, there are many books written with the standard in mind.

10. Why is not IP Pascal compatible with Turbo/Borland®/Dephi®/Kylix Pascal ?
A. IP Pascal was designed to follow the original Pascal standard since 1980, following Niklaus Wirth's "The Pascal User Manual and report" [Jensen and Wirth] from 1974. In 1983, the ISO 7185 standard was released, and the minor changes to J&W Pascal were implemented in IP Pascal.
Unfortunately, none of the Borland products followed either the "User Manual and Report" nor the ISO 7185 Pascal standard, even though it preceeded Borland® implementations by a decade. Borland® products have a large user base, and we respect that, and hope to provide tools to convert user's Borland® compatible products to IP Pascal for interoperation.
For IP Pascal to have been compatible with Borland® products, considerable changes away from standard Pascal would have been required. Also, since there is no official published Borland® language standard, there would be no way to guarantee perfect compatibility with Borland® products. Finally, IP Pascal is directed at a long term standard implementation. Borland® products have traditionally been machine and operating system dependent. The different Borland products, Turbo Pascal, Borland® Pascal, Borland® Windows Pascal, Delphi® and Kylix, are not completely compatible with each other, and would have been a moving target during the many years IP Pascal has been in operation.
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