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Defining New Types in Pascal: A Programmer's Guide

Learn how to create and declare new types in Pascal, including enumerated types and subranges, with examples and operations.

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Defining New Types in Pascal: A Programmer's Guide

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  1. Introduction To Defining New Types in Pascal In this section of notes you how and why programmers can define new types.

  2. Declaring Types • Why bother? • Creating your own type of variable • Making a synonym for an existing type • Format: • Type • Name(1) = Type for name (1); • Name(2) = Type for name (2); • : : : : • Name(n) = Type for name (n);

  3. Declaring Types (2) • Can be used to provide alternative names for existing types • Example: • type • FloatingPoint = real; • var • gpa : FloatingPoint; • income: real;

  4. Declaring Types (2) • Can be used to provide alternative names for existing types • Example: • type • FloatingPoint = real; • var • gpa : FloatingPoint; • income: real; Declaring the type - defining what the type consists of (creating type) Declaring a variable of the new type (creating instances)

  5. Declaring Types (3) • Can be used to provide alternative names for existing types • Example: • type • FloatingPoint = real; • var • gpa : FloatingPoint; • income: real; Original type still usable

  6. Header Declarations const (* Declaration of constants) type (* Declaration of new types *) var (* Declaration of global variables *) (* Declarations of functions & procedures – defining what they do *) Statements begin : end. Where Type Declarations Fit Into Pascal Programs

  7. Programmer-Defined Ordinal Types • Enumerated types • Subrange

  8. Enumerated Types • Format: • Type • Name of type = (identifier 1, identifier 2..identifier n); • Example: • type • Months = (January, February, March, April, May, June, July, August, September, October, November, December); • Budget = array [January..December] of real; • begin • var tamjBudget : Budget; • var monthsIndex : Months; • for monthsIndex := January to December do • tamjBudget[monthsIndex] := 2000 + random(2000); • end.

  9. Operations On Enumerated Types

  10. Examples Of Operations On Enumerated Types • Pred • if ((pred(February)) = January) then • writeln('Jan comes before Feb'); • Ord • writeln(ord(January)); • (As an ASCII converter) writeln(ord('A')); writeln(ord (chr(65))); writeln(chr(65));

  11. Subrange • Used to define a new type which is a subset of an existing type. • Syntax: • type • Subrange name = first value..last value; • Example: • type • Months = (January, February, March, April, May, June, July, August, September, October, November, December); • FallTerm = September..December; • WinterTerm = January..April;

  12. You Should Now Know • Why you need to create your own types • How and where programmer defined types are created • How to define and declare instances of enumerated types and subranges • How to use enumerated types and subranges • What operations are valid on enumerated types and how does each one work

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