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eXercise #15


Compound Data Structures - The ARRAY

Vectors - One Dimensional Arrays

  1. Given the definitions and declarations
    	const	Last-position	=	30;
    
    	type	Indices		=	1.. last_position;
    		Whole		=	0..maxint;
    		Letters		=	'A'..'Z';
    		Messages		=	array [ indices] of char;
    		Distributions	=	array [letters] of whole;
    
    	var	Message		:	messages;
    		FrequencyOf	:	distributions;
    
    and the assignment
    	Message := 'THIS IS A SAMPLE LINE OF TEXT.'
    
    1. Write a function called SpacesIn which scans the Message vector and returns the number of spaces.

    2. Write a small fragment of code which sets every element of the vector FrequencyOf to zero.

    3. Write a procedure called Scan which scans the character vector Message and counts the number of times each letter appears in the vector.

    4. Write a Function called HowMany, that accepts a character and returns the number of times that character appears int he message

      Test this procedure, HowMany('A') should return the value 2 because there are two 'A's in Message, while HowMany('B') should return the value 0 because 'B' does not appear in Message.

    5. Using the FrequencyOf array, store the number of each letter of the alphabet that occurs in the message (FrequencyOf[1] should store the number of 'A's, FrequencyOf[2] should store the number of 'B's and so on) - try to be as efficient as possible in this tallying process. Declare whatever additional variables you require.

    6. Write a procedure called PlotDistribution which scans the vector FrequencyOf and which draws a bar graph of asterisks (representing the numbers stored there) as follows.
      	A	**
      	B
      	C	
      	D
      	E	***
      	F	*
      	:
      


  2. Write a program which prints out the first 13 rows of Pascalls triangle. For your reference, the first few rows are:
    	1
    	1  1
    	1  2  1
    	1  3  3  1
    	1  4  6  4  1
    

Strings - One Dimensonal Arrays of Char

  1. Given the declarations
    	var	reply	:	string[80];
    		1, n	:	integer;
    		r	:	real;
    
    and the assignment
    	reply := 'the albatross did not signify'
    
    determine the value of
    1. reply [1]

    2. ord (reply[0])

    3. reply [length(reply)]

    4. copy (reply,6,5)

    5. length (copy (reply,12,6))

    6. pos ('ss', reply)

    7. copy (reply,19,1) + copy (reply,20,2)

    8. length (reply+reply)


  2. Use the declarations and assignment of question 1 to determine the new value of reply after the application of the following procedures. In each case, assume that reply has its original value indicated above.


    1. insert ('I think 1, reply, 1)

    2. delete (reply, 22, 7)

    3. delete (reply, length(reply), 1)

    4. insert ('.', reply, length(reply))


  3. Assuming the declarations'of question 1, and the assignment
    	reply := '12345.6+789'
    
    determine the effect of the following calls.


    1. val (copy (reply,2,4), n, 1)

    2. val (copy (reply,4,4), r, 1)

    3. val (copy (reply,5,5), r, 1)

    4. str (17, reply)

    5. str (17:3, reply)

    6. str (28.74:8:0, reply)


  4. Given a string FRED of current length L, how would you obtain


    1. the first n characters of FRED?

    2. the last n characters of FRED?


  5. In each of the questions which follow, you will be asked to write a procedure which will augment Pascal's predefined string handling procedures. Note that, having defined a procedure, you are at liberty to use this in subsequent procedures. You may assume the following definition and declarations.
    	type	string8O	=	string[80];
    	var	S,t,u,a		:	string80;
    		i		:	integer;
    

    Write procedures which:



    1. UpShift (s) Shift any character in a string s to its uppercase equivalent.
      	e.g..	'So 16 me'  becomes 'SO 16 ME'
      


    2. Trim (s) Remove any leading and trailing spaces from a string s.
      	e.g.,	'  Hi there!  '   becomes 'Hi there!'
      


    3. DeBlank (s) Remove all blanks from a string s.
      	e.g.,	'Hi there!  '   becomes  'Hithere!'
      


    4. Collapse (s) Remove multiple spaces from a string s.
      e.g.,	'See where   the multiple   spaces are  '
      	becomes  'See where the multiple spaces are'
      


    5. Overwrite(s,t,i) Substitutes s in string t at position i.
      	e.g.,	a := '1961';
      		overwrite ('73',a,3)            a becomes '1973'
      


    6. Replace (s,t,u) Replaces the first occurrence of string s with string t in string u.
      	e.g.,	a := 'chairman';
      		Replace ('man', 'Person', a)
      
      		a becomes 'chairperson'
      


    7. ReplaceAll (s,t,u) Replaces every occurrence of string s with string t in string u.
      	e.g.,	a := 'The chairman's presence was mandatory' 
      		ReplaceAll ('man', 'person', a)
      
      			a becomes 'The chairperson's presence was persondatory'
      

Multi-Dimensioned Arrays

  1. Noughts and crosses is a game that uses a grid (in this version, a 4x4 array of char) with the winner being the first to get '4 in a row'. You can Download the COMPLETED game by clicking here: tic_tac.exe.

    You can download the PARTIAL SOURCE CODE by clicking here : tic_tac.pas

    Your mission, Jim, should you chose to accept it, is to copy the partial source code file to your working directory and then complete the program so it matches the running one.

    EXTRA FOR EXPERTS: the program as given contains many procedures and functions that are 'impolite' - ie. they clobber GLOBAL variables without being passed them - re-write the procedures and functions so they only use objects they either own or were passed. multi-dim array

  2. Three dimensional Tic_Tac_toe is like it's 2-d counterpart, but more challenging - winning moves can run horizontally, vertically and diagonally through the 'rubic cube - like space' - your challenge is to write it.

    decide first, how to display the workspace - I would suggst you do so in SLICES. The user will need to enter 3 coordinates to claim a cell,you will need to validate their choice, then the fun starts - checking for a win....

Solutions

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