CMP 131 Introduction to Computer Programming Violetta Cavalli-Sforza Week 6, Lecture 1 (Monday)

CMP 131Introduction to Computer

Programming

Violetta Cavalli-Sforza

Week 6, Lecture 1 (Monday)

TODAY

• Flow of control and flow charts

• Conditional statements

• Boolean expressions

• Go over Homework #2 programming part

TOMORROW (Lab)

• Exercises on the computer with I/O and simple conditional statements.

• Review of topics for Midterm Exam

Syntax Graphs, Flowcharts, & Structure Charts

• Syntax graph– To define the language syntax

• Structure chart– To show the relationship between program modules and the data

transfer between the modules (Example)

CONST =Identifier ;value

Compute mean of 3 numbers

Read 3 numbers

Compute mean of inputs

Display mean to screen

http://camss.meen.ncat.edu/camss/structure/chart.htm

• Flowchart– A form of visual control-flow specification

employing arrows and balloons of various shapes.

– Shows flow of actions (algorithm) in a program

How the locus (location) of execution changes as the program executes.

Example. Let Height = 3 and Width = 5

FOR I := 1 to HeightBEGIN

FOR J := 1 TO Width DO write(‘*’); writeln;

END

What is Flow of Control?

007 …008 I := 1009 IF I > 3 GOTO 018010 J := 1 011 IF J > 5 GOTO 015012 write(‘*’)013 J := J + 1014 GOTO 011015 writeln016 I := I + 1017 GOTO 009018 …

DATA MEMORY

I = ?

J = ?


DATA MEMORY

I = 1

J = ?


DATA MEMORY

I = 1

J = 1


DATA MEMORY

I = 1

J = 2

A few steps later …


DATA MEMORY

I = 1

J = 6


DATA MEMORY

I = 2

J = 6


DATA MEMORY

I = 2

J = 1

A few steps later …


DATA MEMORY

I = 3

J = 6


DATA MEMORY

I = 4

J = 6

Flow of Control

• You can show it by animation for the simplest programs or

• You can show it much more succinctly with Flow Charts

• A graphical formalism for showing how control flows through a program

• Standard Flowchart Symbols (later) fromhttp://www.wiley.com/legacy/college/busin/icmis/oakman/outline/chap05/slides/symbols.htm

Flowchart Symbols

Rectangle Flow Chart

I := 1

write(‘*’)

J := 1

J := J+1

I := I+1

I > 3

J > 5 writeln

no

yes

no

yes

BEGIN

END

Yes/No Choice

• The logic:IF some condition or test is TRUETHEN perform some action[ ELSE do nothing ]

• Examples: – If the car is running out of gas, put in gasoline.– If you are failing your class and you cannot drop it,

study more.– If someone says hello and you don’t want to seem

impolite, say hello back.

Yes/No Choice: The IF-THEN Statement

• Syntax: IF <condition> THEN <statement>

• Syntax graph:

• Flowchart:

IF condition THEN statement

statement 1

conditionyes

no

statement 3

statement 2

Either/Or Choice

• The logic:IF some condition or test is TRUETHEN perform some actionELSE perform a different action

• Examples: – If the weather is hot wear light clothes, else wear

warm clothes.– If a number is odd increment OddCount else

increment EvenCount– If a noun starts with a capital letter categorize it as a

proper noun (name) else as a common noun.

Either/Or Choice : The IF-THEN-ELSE Statement

• Syntax: IF <condition> THEN <statement> ELSE <statement>

• Syntax graph:

• Flowchart:

IF condition THEN statement ELSE statement

statement 1

conditionyes

statement 4

statement 2no

statement 3

What is <statement> ?

• A single statement:– An input or output statement– An assignment– Another IF … THEN … ELSE statement– A looping statement (FOR, WHILE, REPEAT)

• A compound statement:BEGIN

<statement> ; <statement> ; ….<statement>

END

What is <condition> ?

• A boolean expression

• Named after the mathematician George Boole who invented logic.

• Boolean expressions – Evaluate to TRUE or FALSE– Include

• different types of operands• different types of operators

Boolean Expressions

• Boolean constants– TRUE– FALSE

• Boolean variables– Declared as type “boolean”

CONSTDebug = TRUE; { or FALSE }

VARSaveDebug : BOOLEAN;

• Relational expressions: Arithmetic, character, or strings acted upon by relational operators: – Relational operators are:

• <= less than or equal to• < less than• >= greater than or equal to• > greater than• = equal• <> not equal

– Relational operators compare two compatible values• Two characters• Two strings• Real and integer• Two Booleans

– Relational operators return a Boolean value

• Examples: new < old

‘B’ < ‘A’

value <> -99999

3.0 < 4

MiddleInitial = ‘L’

1.0 = 1.0/ 3.0 * 3.0 { Implementation dependent}

• Logical expressions: Boolean values acted upon by logical operators– Logical operators are:

• AND• OR• NOT

– Logical operators take Boolean operands and return Boolean values.

– Examples:• IF NeedMoney AND

(NOT HaveMoneyInHand) AND HAVE MoneyInBankTHEN {Go get money at the bank}ELSE {Ask parents for money}

• IF Value < MinValue OR Value > MaxValue THEN writeln (‘Value ‘, Value, ‘ is out of range.’)

Truth Tables for Boolean Operators

Op1 Op2 Op1 AND Op2 Op1 OR Op2 NOT Op1 true true true true false

true false false true false

false true false true true

false false false false true

binary operators unary operator

Operator Precedence: Arithmetic, Relational and Logical

Operator Precedence( ) parentheses Highest (evaluated

first)

- + NOT (unary operators)

* / DIV MOD AND

+ - OR

< <= = <> >= > Lowest (evaluated last)

(4.2 >= 5.0) AND (8 = (3 + 5)) (4.2 >= 5.0) OR (8 = (3 + 5))

writeln('Value of (-2 < 0) AND (18 >= 10) is : ', (-2 < 0) AND (18 >= 10) ); writeln('Value of (-2 < 0) OR (18 >= 10) is : ', (-2 < 0) OR (18 >= 10) ); writeln('Value of (3 > 5) AND (14.1 = 0.0) is : ', (3 > 5) AND (14.1 = 0.0) ); writeln('Value of (3 > 5) OR (14.1 = 0.0) is : ', (3 > 5) OR (14.1 = 0.0) ); writeln('Value of NOT (18 = 10 + 8) is : ', NOT (18 = 10 + 8) ); writeln('Value of NOT (-4 > 0) is : ', NOT (-4 > 0) ); writeln('Value of ''a'' < ''b'' is : ', 'a' < 'b' ); writeln('Value of ''a'' < ''A'' is : ', 'a' < 'A' );

Summary of Operations on Boolean Values

• Logical operations (AND, OR, NOT)– Relational operators act on non-Boolean

values but return Boolean values• Assignment

VAR Debug, SaveDebug : BOOLEAN;Debug := TRUE;SaveDebug := Debug; {Save the value of Debug}

• Output (in Turbo Pascal)writeln (‘The value of Debug is ‘, Debug);

• (Not Input – can’t read/readln a Boolean value)

Boolean expressions

• Appear primarily in control structures• Used to determine the sequence in which Pascal

statement are executed.• Boolean variables are often called Boolean ‘flags’ :

varDebug, SaveDebug : Boolean;…

BEGIN…SaveDebug := Debug;Debug := TRUE;IF Debug THEN {print out the value of several variables}Debug := SaveDebug;...

END

Example Expressions

• See program BOOLEXPR.PAS

Go Over Homework #2, Programming Part

Exercises 1.5, #13

• Write a complete program that produces the following table:

WIDTH LENGTH AREA

4 2 8

21 5 105

Task Decomposition (1)

• Write table header: WIDTH LENGTH AREA

• Write table contents: 4 2 8

21 5 105

• Simplest codewriteln(‘WIDTH LENGTH AREA’);

writeln(‘ 4 2 8’);

writeln(‘ 21 5 105’);

Using formatting

• Assume table header starts in first column 1:• Write header as

– WIDTH, 8 spaces, LENGTH, 8 spaces, AREA• Write columns of numbers as

– First number fits in field of width 3– Second number fits in field 2+8+4 = 14– Third column fits in field of 2+8+4 = 14

• Code will bewriteln(‘WIDTH’,‘ ’:8,‘LENGTH’,‘ ’:8,‘AREA’);writeln(4:3,2:14,8:14);writeln(21:3,5:14,105:14);

Exercises 1.5, #8

• Assume the hourly wages of five students are: 3.65, 4.10, 2.89, 5.00, 4.50. Write a program that produces the following output, where the “E” in Employees is in column 20.

Desired Output

12345678901234567890123456789012345678901234

-------------------------

Employees Hourly Wage

-------------------------

1 $ 3.65

2 $ 4.10

3 $ 2.89

4 $ 5.00

5 $ 4.50

-------------------------


• Write table header:

------------------------- Employees Hourly Wage -------------------------

• Write table contents:

1 $ 3.65

….• Write table footer: -------------------------

Task Decomposition (2)• Write table header:

– Write line starting at column 20– Write column headings starting at column 20– Write line starting at column 20


• Write table contents:– Write 5 lines each with:

• Employee number starting at column 23• Employee wage starting at column 36

1 $ 3.65

….• Write table footer:

– Write line starting at column 20 -------------------------


• Write table header:– Write line starting at column 20– Write column headings starting at column 20– Write line starting at column 20


• Pascal code:– CONST Line = ‘-------------------------’– BEGIN

writeln(‘ ’:19,Line); writeln(‘ ’:19,‘Employee’,‘ ’:5,‘Hourly Wage’);

writeln(‘ ’:19,Line); … END.

Task Decomposition (4)• Write table contents:

– Write 5 lines each with:• Employee number starting at column 23• Employee wage starting at column 36

1 $ 3.65

….• Pascal code:

– BEGIN…

writeln(1:23,‘$’:13,3.65:5:2); writeln(2:23,‘$’:13,4.10:5:2);

writeln(3:23,‘$’:13,2.89:5:2); writeln(4:23,‘$’:13,5.00:5:2); writeln(5:23,‘$’:13,4.50:5:2);

… END.


• Write table footer:– Write line starting at column 20

-------------------------

• Pascal code:– CONST Line = ‘-------------------------’– BEGIN

...

writeln(‘ ’:19,Line);

END.

CMP 131 Introduction to Computer Programming Violetta Cavalli-Sforza Week 6, Lecture 1 (Monday)

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