Chapter 13

Answers to Exam Preparation Exercises

2. Algorithm sketches:

(a) The indices of the Sales array have semantic content. After setting Sales to all zeros, read in a Code and an Amount. The statement

Sales[Code] := Sales[Code] + Amount

will increment the total for the proper category.

(b) This is an arrays of records problem. The master file must be read into an array of records. The second file is read one record at a time. The ID number of the current record is used to find the associated payroll information in the array of records.

3. (a) valid (b) valid (c) valid (d) valid (e) invalid (f) invalid (g) valid

5. Declarations

CONST

Max_Number = 1000;

TYPE

(a) Car_Type = (Ford, Honda, Jaguar, Renault, Saab);

(b) Inventory_Range = 1..Max_Number;

Inventory = ARRAY[Inventory_Range] OF Car_Type;

(c) VAR

Cars : Inventory;

6. (a) valid (b) invalid (c) valid (d) invalid (e) valid (f) invalid

7. (a) Print each book borrowed by Name

FOR Counter := 1 TO Books.Length DO

IF Books.Borrower[Counter] = Name

THEN Write(Books.Title[Counter])

(b) Count books borrowed by Name

Books_Borrowed := 0;

FOR Counter := 1 TO Books.Length DO

IF Books.Borrower[Counter] = Name

THEN Books_Borrowed := Books_Borrowed + 1

(c) Count number of copies of Book_In borrowed

Number_Of_Copies := 0;

FOR Counter := 1 TO Books.Length DO

IF Books.Title[Counter] = Book_In

THEN Number_Of_Copies := Number_Of_Copies + 1

(d) Count copies of Book_In borrowed by Name

Number_Of_Copies := 0;

FOR Counter := 1 TO Books.Length DO

IF (Books.Title[Counter] = Book_In) AND

(Books.Borrower[Counter] = Name)

THEN Number_Of_Copies := Number_Of_Copies + 1

(e) Print the names of those who have books checked out

FOR Counter := 1 TO Books.Length DO

Writeln(Books.Borrower[Counter])

(f) Does Chipendale have a book checked out?

Name := 'Chipendale ';

CheckedOut := False;

Counter := 0;

WHILE NOT CheckedOut AND Counter <= Books.Length DO

IF Books.Borrower[Counter] = Name

THEN CheckedOut := True

ELSE Counter := Counter + 1;

IF CheckedOut

THEN Writeln('Chipendale has a book checked out.')

ELSE Writeln('Chipendale doesn't have a book checked out.');

(g) Is Gone with the Wind checked out?

Book_In := 'Gone with the Wind ';

CheckedOut := False;

Counter := 0;

WHILE NOT CheckedOut AND Counter <= Books.Length DO

IF Books.Title[Counter] = Book_In

THEN CheckedOut := True

ELSE Counter := Counter + 1;

IF CheckedOut

THEN Writeln('Gone with the Wind is checked out.')

ELSE Writeln('Gone with the Wind is not checked out.');

9. Number of comparisons:

Item Is_There2 Is_There_Ordered

28 1 1

32 10 2

196 7 7

194 10 7

Answers to Programming Warm-Up Exercises

2. Procedure Take_Product:

PROCEDURE Take_Product ( A, B : Int_Ary;

Vector_Length : Integer;

VAR Product : Integer);

VAR

Counter: Integer;

BEGIN (* Take_Product *)

Product := 1;

FOR Counter := 1 TO Vector_Length DO

IF A[Counter] < 0

THEN Product := Product * B[Counter]

END; (* Take_Product *)

3. Function Found.

FUNCTION Found (List : ListType; Item: Real) : Boolean

VAR

Counter : Integer;

BEGIN (* Found *)

Found := False;

Counter := 1;

WHILE NOT Found AND (Counter <= List.Length) DO

IF Item = List.Items[Counter]

THEN Found := True

ELSE Counter := Counter + 1

END; (* Found *)

6. No changes are necessary.

7. Procedure to delete all occurrences of Item:

PROCEDURE Delete_All (VAR List: List_Type;

Item: Item_Type);

(* Pre: List has been initialized *)

(* Post: No copies of item exist in List *)

VAR

Found: Boolean;

Counter: Integer;

BEGIN (* Delete_All *)

REPEAT

Counter := 1;

Found := False;

WHILE (Counter <= List.Length) AND NOT Found DO

IF List.Items[Counter] = Item

THEN Found := True

ELSE Counter := Counter + 1;

IF Found

THEN

BEGIN

FOR Counter := Counter TO List.Length - 1 DO

List[Counter] := List[Counter + 1];

List.Length := List.Length - 1

END

UNTIL NOT Found

END; (* Delete_All *)

8. Procedure Copy_List

PROCEDURE Copy_List(VAR Out_List : List_Type;

In_List : List_Type);

BEGIN (* Copy_List *)

Out_List := In_List

END; (* Copy_List *)

In Chapter 17 we introduce another list implementation for which a simple assignment statement doesn't work.

9. Parallel list example:

PROCEDURE Set_Score (VAR Score: Real_List_Type;

Present: Boolean_List_Type);

(* Pre: Score and Present are the same length *)

VAR

Counter: Integer;

BEGIN (* Set_Score *)

FOR Counter := 1 TO Present.Length DO

IF Present.Items[Counter]

THEN Score.Items[Counter] := 0.0

END; (* Set_Score *)

12. Alternate insertion algorithm

PROCEDURE Insert_Alt(VAR List: List_Type; Item: Item_Type);

VAR

Counter : Integer;

Place_Found : Boolean;

BEGIN (* Insert_Alt *)

Counter := 1;

WHILE NOT Place_Found AND (Counter <= List.Length) DO

IF Item < List.Items[Counter]

THEN Counter := Counter + 1

ELSE Place_Found := True;

FOR Counter := List.Length DOWNTO Counter DO

List.Items[Counter + 1] := List.Items[Counter];

List.Items[Counter] := Item;

List.Length := List.Length + 1

END; (* Insert_Alt *)

13. Comparison of two lists

FUNCTION Identical(List1, List2 : List_Type) : Boolean;

VAR

Counter : Integer;

Still_The_Same : Boolean;

BEGIN (* Identical *)

Counter := 1;

Still_The_Same := List1.Length = List2.Length;

WHILE Still_The_Same AND (Counter <= List1.Length) DO

IF List1.Items[Counter] <> List2.Items[Counter]

THEN Still_The_Same := False

ELSE Counter := Counter + 1;

Identical := Still_The_Same

END; (* Identical *)