CMP 131Introduction to Computer

Programming

Violetta Cavalli-Sforza

Week 2, Lecture 2

Case Study 1Converting Units of Measurements

• Problem Statement You work in a store that sells

imported fabric, measured in square meters; The store customer wants to know the equivalent amount in square yards. You need to write a program that performs the conversion.

Case Study 1Converting Units of Measurements

• Analysis:

– Input:

• Fabric size in square meters (SqMeters).

– Output:

• Equivalent amount in square yards (SqYards).

– Relevant Formulas:

• The relationship between sq. meter & sq. yards

• (1 m2 = 1.196 y2)

Case Study 1Converting Units of Measurements

• Design:

– Algorithm:

1. Read the fabric size in m2.

2. Convert size to yd2 using the formula (1 m2 = 1.196 y2).

3. Display fabric size in yd2.

– Refinement of step2:

2.1 Fabric size in yd2 = 1.196 * fabric size in m2

Case Study 1 Converting Units of Measurements

• Implementation– Program header

• Give a logical name for your program– Program Name:ConvertSqMtoSqYd;

• The name of the source code file of the program can be different from the logical name

– File name: CONVMYSQ.PAS– TurboPascal limits file names to 8 characters

– Declaration section• Memory cells used in your program• Constant declaration: use constants for unchanged

values• Variable declaration: use variables for values that

change– Program body

• Data processing takes place here

Case Study 1Converting Units of Measurements• Implementation (Using Turbo Pascal)

program ConvertSqMtoSqYd;{Convert square meters to square yards }const MetersToYards = 1.96; {conversion

constant}var SqMeters, {input - fabric size

in meters}SqYards : real; {output - fabric size

in yards}begin{Read the fabric size in square meters.}

WriteLn ('Enter the fabric size in square meters >');ReadLn(SqMeters);

{Convert the fabric size to square yards.}SqYards := MetersToYards * SqMeters;

{Display the fabric size in square yards. }WriteLn ('The fabric size in square yards is ', SqYards)

end.

Case Study 1Converting Units of Measurements

• Testing (Output Window):– A program run

Enter the fabric size in square meters > 2.00The fabric size in square yards is 2.392000E+00

Case Study 2: Square & Cube

• Problem Statement– Write a program that calculates the square root, square,

and cube of a number

• Is this statement clear & sufficient for analysis & design steps?– NO

Case Study 2: Square & Cube

• Modified Problem Statement Write a program that gets an integer number

from the user, calculates the square root, square and cube of the number and then prints the number,the square root, the square, and the cube. If the number is negative, the square root should not be evaluated. An error message should be written instead. The output should be labeled with suitable headings.

Case Study 2: Square & Cube• Analysis

– Input • Get a number from the user

– Processing & formulas• Calculate the square root, the square, & the cube

– SquareRoot = sqrt(Number) – Square = Number x Number.– Cube = Number x Square.

– Output • Write labels for Number, Square root, Square, and Cube• Write values of Number, Square root, Square, and Cube

(This is one way of doing it…)

Case Study 2: Square & Cube

• Design (Algorithm)

1.Pseudocode for initializationClear screenWrite program purpose

2. Pseudocode for Input Read Number

3. Pseudocode for Processing SquareRoot = Sqrt(Number)Square = Number * Number Cube = Square * Number

4. Pseudocode for Output Write “Number”, “Sq. Root”,“Square”, “Cube”Write Number, SquareRoot, Square, Cube

5. Pseudocode for terminationWrite Goodbye message

Case Study 2: Square & Cube• Implementation

– Program header

program SquareNCube;

– Declaration section

constHEAD = ‘Number Sq.Root Square Cube’; { Heading }

var Number, { input- number being processed }Square, { output - square of the number } Cube : integer; { output- cube of the number }SquareRoot : real; {output- square root of the

number}

– Program body

Case Study 2: Square & Cube

• Implementation: First draft– Program Body

• Enclosed between begin & end.• Write algorithm as comments

begin {Program body}

{1. Initialize}{2. Read Number }

{3. Calculations / Evaluate formulas}{4. Output heading & values}

{5. Terminate}

end.

Case Study 2: Square & Cube• Implementation: Second draft

Add Pascal statements in corresponding places

begin {Program body}{1. Initialize}

Clrscr;WriteLn(‘This program calculates square rt., ‘);WriteLn(‘square & cube of a given number’);

{2. Read Number } write (‘Enter a number ’); readln (Number); {3. Evaluate formulas}

if (Number >= 0) then SquareRoot := sqrt(Number)else WriteLn(‘Square root can't accept negative values’);

Square := Number * Number; {evaluate square}Cube := Square * Number; {evaluate cube}

{4. Output heading & values} { writeln ( HEAD ); } writeln (‘Number Sq.Root Square Cube’); writeln ( Number, SquareRoot, Square, Cube )

{5. Terminate}WriteLn(‘Good bye’);ReadLn;

end.

Case Study 2: Square & Cube• Implementation: (Final Pascal Code)

program SquareNCube; const { Declaration part }

HEAD = ‘N umber Sq.Root Square Cube’; { Heading } var

Number, { input- number being processed }Square, { output - square of the number } Cube : integer; { output- cube of the number }SquareRoot : Real; {output- square root of the number}

begin { Program body }{ Initialize}

Clrscr;WriteLn(‘This program calculates square rt., ‘);WriteLn(‘square & cube of a given number’);

{ Read Number } write (‘Enter a number’); readln (Number); { Evaluate formulas }

if (Number >= 0)then SquareRoot := sqrt(Number)else WriteLn(‘Square root can't accept –ve values’);Square := Number * Number; { evaluate square }Cube := Square * Number; { evaluate cube }

{ Output heading & values } writeln ( HEAD ); writeln ( Number, SquareRoot:6:2,Square, Cube );{ Terminate}

WriteLn(‘Good bye’);ReadLn;

end. { end of program body }

Ideas from Students• A program for keeping track of my grades in a course

– Easy• A program like those in graphic calculators that allows

entering the data and will automatically display mean/average, the frequency, the median, the mode … – Easy, we’ll do a simple version of it

• A special dictionary that will enable me to write customized terms and the computer will automatically recognize the word I meant and transform it by itself. Ex: dvlp would stand for development. That would be very time saving while writing reports.– Not hard, but in this course we don’t learn everything we need

• A program for planning courses: what courses do I take next and what courses do I have left.– A planning and scheduling problem, can be arbitrarily hard

• A program for managing my time and schedule– If you know an algorithm for doing that, let me know….

A Limitation

• In this course, given the syllabus, we are limited to solving problems where you know beforehand how many inputs you will have or where you do not have to keep track of the values of individual inputs (unless you use external files to do so).

• Why?– Because we will look at only a limited set of

ways of representing data in memory

Case Study 3: Keeping Track of Grades in a Course

• A program for keeping track of my grades in a course– Is this specified clearly enough?

Case Study 3: Revised Problem Statement

A program that will let me enter and store the score that I receive for each assessment in the course, the maximum score that I could have obtained in that assessment, and the name of the assessment. When I run the program, it will retrieve and display the scores it already knows and give me the option to enter the new data. When I exit the program, all the data (old and new) will be stored to a file so that it can be retrieved next time the program is run.

Case Study 3: Begin Analysis

A program that will let me enter and store the score that I receive for each assessment in the course, the maximum score that I could have obtained in that assessment, and the name of the assessment. When I run the program, it will retrieve and display the scores it already knows and give me the option to enter the new data. When I exit the program, all the data (old and new) will be stored to a file so that it can be retrieved next time the program is run.

Case Study 3: I/O Analysis

• Input:• Existing data from file• New data from keyboard

• Output:• Existing data plus new data to file

Case Study 3: Processing Analysis• Processing:

– Display existing data• Decide: about how to display the data.

E.g. Table with headers: Assessment My Score Max Score HW#1 8 10 …. … ….

– Prompt for new data:• Data: Name of assessment, My score, Max score• Decide:

– prompt for data one by one or all 3 at a time?– prompt for data for a single assessment or multiple assessments?

If multiple assessments, how do you indicate you are done?– Store old and new data:

• Decide: – Overwrite the old file?– Make a new version of the file?

• Decide:– Display all the data the program knows about before exiting?

Case Study 3: Revised Problem Statement

• A program that will let me enter and store the score that I receive for each assessment in the course, the maximum score that I could have obtained in that assessment, and the name of the assessment. When I run the program, it will:– Retrieve and display the scores it already knows in a table with

suitable headers – Give me the option to enter data for one or more additional

assessments or to exit– If I choose to enter data for an assessment it will prompt me for

all three values on one line– After I enter the values it will again give me the option to enter

new data or to exit.• When I exit the program

– all the data (old and new) will be stored to a new file so that it can be retrieved next time the program is run.

– all the data it has for me will be shown.

Are you starting to think that you should use a spreadsheet instead?