Pascal

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 ltgt Sentinel do begin
• writeln(Trunc(X) 17, Round(X) 10, Abs(X)
  102, Sqrt(X) 102)
• 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 gt 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 gt 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

13
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