Class Notes: Computer Programming in Pascal

Fall 1997 - Tue 8-9th Period, Thu 9th Period CSE/E221

Instructor: M.S. Schmalz

Project 5 Assignment

• Goal. The purpose of this project is to learn about sorting, arrays, and loops by getting hands-on experience with Turbo PASCAL.

• Statements. We will be using the following programming statements: Program, Var (for scalars and arrays), Procedure, If-Then-Else, For, ReadLn and WriteLn.

• Features. We will be making a procedure that uses scalar variables and arrays and is encapsulated in modular form, and uses nested loops to sort an array of numbers, as discussed in class.

• Concept. The program Proj5 will (a) input a list of numbers from the keyboard, (b) sort the numbers in ascending order, and (c) output the sorted list to the screen.

• Algorithm. Program 5 will be structured according to the following pseudocode description:

  -------| PROGRAM P-CODE |---------------    -------| IN-LINE COMMENTS |-------
  PROGRAM Proj5:                               ## CGS 2462 - Program 5: Sorting
    DECLARE  a,b,c : array [1..10] of integer  ## Declare global arrays
  	   i     : integer                   ## Declare array index
    END-DECLARE  
  
    BEGIN-PROGRAM-BODY
  
      WRITELN('>>> Enter 10 numbers [0..100] on one line, separated by spaces')
  
      FOR i = 1 TO 10 DO                       ## Input ten numbers from keybd
        READ(a[i])
        c[i] := a[i]                           ## Make copy of a for output
      ENDFOR
  
      BubbleSort(10)                           ## Sort numbers in ascending order
  
      FOR i = 1 TO 10 DO                       ## Output numbers and sorted
        WRITELN('   INPUT          OUTPUT')    ## numbers to screen
        WRITELN('a[',i,'] = ', c[i], '  b[',i,'] = ', b[i])
      ENDFOR
  
    END-PROGRAM-BODY
  
  PROCEDURE BubbleSort(N):                     ## CGS 2462 - Bubble Sorting Proc.
    DECLARE  N,minimum,maximum  : integer      ## Declare local bounds
             i,j,imin,imax,flag : integer      ## Declare loop indices
    END-DECLARE
  
    BEGIN-PROCEDURE-BODY
  
      minimum := 9999                          ## Set bounds and flag values
      flag    := minimum
  
      FOR j = 1 TO N DO:                       ## For each of N input data
  
        FOR i = 1 TO N DO:                     ## Search for the array minimum
          IF ( a[i] < minimum ) THEN
            minimum := a[i]                    
            imin    := i                       ## Save the location where
          ENDIF                                ##   minimum was found
        ENDFOR
  
        b[j]    := a[imin]                     ## Put the found min. in output
        a[imin] := flag                        ## Reset the input minimum
      ENDFOR
  
    END-PROCEDURE-BODY
  

• PASCAL Programming Procedure. Enter the preceding p-code in Pascal form using Turbo PASCAL, as we did in class. Here are a few hints that will help you. Follow the directions at the bottom of the page for handing in your project materials:
  Step 1. The arrays a and b are global arrays, so you don't have to worry about passing them through the argument list of the Procedure.

  Step 2. Be careful with BEGIN and END statements! Remember that they delimit a functional block. If there are multiple statements within a FOR or IF statement, then that block of statements must be delimited by BEGIN and END statements. In the preceding p-code example, I use BEGIN-PROGRAM-BODY and END-PROGRAM-BODY for this purpose, and symmetrically for the procedure body.

  Step 3. Based on your experience with errors in Project 4, and our discussion in class, check to see if there are any errors in the preceding program statements. Since we discussed the code in detail in class, I have removed some of the mistakes and revised the array declarations, to make the project a little easier. However, you still need to check for missing semicolons, or wrong variable names, etc.

  Run the program with test numbers and see if the output is correct. If the output is sorted incorrectly, why does this occur? Hint: Trace the p-code example, above, to verify its functionality.

  Step 4. Run the program with the following test data:

  20 43 68 57 44 25 22 20 34 44
  

  Your output should have the following form:

     INPUT       OUTPUT
   a[1] = 20   b[1]  = 20
   a[2] = 43   b[2]  = 20
   a[3] = 68   b[3]  = 22
   a[4] = 57   b[4]  = 25
   a[5] = 44   b[5]  = 34
   a[6] = 25   b[6]  = 43
   a[7] = 22   b[7]  = 44
   a[8] = 20   b[8]  = 44
   a[9] = 34   b[9]  = 57
   a[10] = 44   b[10]  = 68
  

  Now, run the program with ten integers of your choosing, ranging from 0 to 100.

  Step 5. Document the program produced in Step 1 by inserting in-line comments using braces ( {} ), and comments in separate lines before the procedure. A few examples of in-line comments have been shown in the p-code. You will have to convert the procedure in-line comment to a properly structured comment on its own line.

• Hardcopy. The completed program (Proj5 together with the two output lists) should be printed on a CIRCA 24-pin printer, or a good-quality printer you may have at home. Laser printer output is acceptable, if you have access to a laser printer. Otherwise, a 24-pin dot matrix printer will do. Output should be dark, so I can read the print. Staple your two pages (one program, one output page) together and write your NAME, SSN, CGS2462, and today's DATE at the TOP RIGHT-HAND CORNER of the paper, in BIG BLOCK LETTERS (so I will not mistake it for someone else's). Be sure to print clearly, so I will know whose program it is.

• Items Due. Give the instructor your completed project hardcopy in class on Thursday 13 November 97. Projects turned in a day late will be penalized -10%; two days late: -20%. Projects turned in after the Friday following the due date will not be accepted unless accompanied by a documented excuse (note from your physician or advisor).