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Pascal

Pascal. Regina Bellamy Katitia Eaddy Corinthia Cunningham Anthony Mancuso. Problem Domain. Designed to be efficient and concise First developed for instructional use Later extended for more wide-spread use. Historical Context.

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Pascal

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  1. Pascal Regina Bellamy Katitia Eaddy Corinthia Cunningham Anthony Mancuso

  2. Problem Domain • Designed to be efficient and concise • First developed for instructional use • Later extended for more wide-spread use

  3. Historical Context • Developed by Nicklaus Wirth after Algol-W passed up for Algol-68 • Named after Blaise Pascal, a French mathematician • Direct descendent from Algol-60 and Algol-W in 1971 • Used from the late 60s to the late 80s for teaching programming, which it was originally designed for

  4. Evolution of the Language • Pascal was extended to better support the needs of programmers • Pascal-P (Portable) was created to allow code to be ported to various operating systems (virtual machine!) • Borland and Apple created object-oriented extensions in the 1990s • Borland then created Delphi, which uses Pascal as its programming language • ML and Modula are descended from Pascal

  5. Language Concepts • Case-insensitive • Semicolon as a separator • Functions and procedures • Variable-length strings vs. arrays of characters • Record (borrowed from COBOL) • Repeat..until (do..while in C) • In

  6. Example 1 – A Sample Program Program ArithFunc; const Sentinel = 0.0; var X : Real; begin writeln(‘Enter a real number, 0.0 to stop’); writeln; writeln(‘X’, ‘Trunc(x)’ :16, ‘Round(x)’ :10, ‘Sqrt(Abs(X))’ :15); readln(X); while X <> Sentinel do begin writeln(Trunc(X) :17, Round(X) :10, Abs(X) :10:2, Sqrt(X) :10:2); readln(X) end end. Reference: http://pascal-central.com/ppl/chapter4.html

  7. Example 2 – Using Procedures Program Something; procedure DoSomethingElse(x : real); begin writeln(‘Displaying half of your number: ’, x / 2) end; procedure DoSomething; var x : real; begin writeln(‘Enter a number.’); readln(x); DoSomethingElse(x) end; begin DoSomething end.

  8. Example 3 – While Version Program FactorialWhile; var n, fact : integer; begin writeln(‘Enter n to compute n!.’); readln(n); fact := 1; while n > 1 do begin fact := fact * n; n := n – 1 end end.

  9. Example 3 – Repeat Version Program FactorialRepeat; var n, fact : integer; begin writeln(‘Enter n to compute n!.’); readln(n); if n > 0 then begin fact := 1; repeat fact := fact * n; n := n – 1; until n = 0; end end.

  10. Example 3 – Downto Version Program FactorialFor; var n, i, fact : integer; begin writeln(‘Enter n to compute n!.’); readln(n); fact := 1; for i := n downto 1 do fact := fact * i end.

  11. Comparison to Algol • Designed to be simpler than its ancestor • Algol-60 was the first block-structured language • Foundation provided by Algol-W

  12. Comparison to C • Record vs. struct • Variable-length string vs. char[] • Begin..end vs. { } • Pascal is more strongly typed • Pascal allows nested function definitions

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