James Tam Introduction To Defining New Types in Pascal In this section of notes you will learn about programmer-defined types.

James Tam Declaring Types Why bother? Needed to pass arrays as parameters Creating your own type of variable Making a synonym for an existing type Syntax: Type Name(1) = Type for name (1); Name(2) = Type for name (2); : : : : Name(n) = Type for name (n);

James Tam Declaring Types (2) Example: type Board = array [1..8,1..8] of char; var chessBoard : Board; checkerBoard: Board;

James Tam Declaring Types (2) Example: Type Board = array [1..8,1..8] of char; Var chessBoard : Board; checkerBoard: Board; Declaring the type - defining what the type consists of Declaring variables of the new type

James Tam Declaring Types (3) Needed to pass arrays as parameters This won't work procedure proc (chessBoard : array of char); begin : end; A specific type needs to be passed in procedure proc (chessBoard : Board); begin : end; Not a type! Programmer-defined type Composite types like arrays cannot be returned from functions

James Tam Declaring Types (4) Can be used to provide alternative names for existing types Example: type FloatingPoint = real; var gpa : FloatingPoint; income: real;

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

James Tam Where Type Declarations Fit Into Pascal Programs program name; (* Declarations *) const (* Declaration of constants) type (* Declaration of new types *) var (* Declaration of variables *) (* Declarations of functions & procedures – defining what they do *) begin end.

James Tam Ordinal Types Enumerated types Subranges

James Tam Enumerated Types Syntax 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; var tamjBudget : Budget; monthsIndex : Months; begin for monthsIndex := January to December do begin tamjBudget[monthsIndex] := Random(2000); end; end.

James Tam Operations On Enumerated Types OperationName Equity= Inequity<> Less than< Less than, equal to<= Greater than> Greater than, equal to>= Predecessorpred Successorsucc Ordinal Numberord

James Tam 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) ord('A'); ord (chr(65))

James Tam Subranges Used to define a new type which is a subset of an existing type. Syntax: type Subrange name = first value..last value; Example: type FallTerm = September..December; WinterTerm = January..April;

James Tam Summary You should now know how to define new, ordinal, types in Pascal programs.