CMP 131 Introduction to Computer Programming

1
CMP 131Introduction to Computer Programming

• Violetta Cavalli-Sforza
• Week 6, Lecture 1 (Monday)

2
TODAY

• Flow of control and flow charts
• Conditional statements
• Boolean expressions
• Go over Homework 2 programming part

3
TOMORROW (Lab)

• Exercises on the computer with I/O and simple
  conditional statements.
• Review of topics for Midterm Exam

4
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)

Compute mean of 3 numbers
Read 3 numbers
Compute mean of inputs
Display mean to screen
5

• Flowchart
• A form of visual control-flow specification
  employing arrows and balloons of various shapes.
• Shows flow of actions (algorithm) in a program

6
What is Flow of Control?

• How the locus (location) of execution changes as
  the program executes.
• Example. Let Height 3 and Width 5
• FOR I 1 to Height BEGIN FOR J 1 TO
  Width DO write() writeln END

7
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I ?
J ?
8
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 1
J ?
9
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 1
J ?
10
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 1
J 1
11
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 1
J 1
12
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 1
J 1
13
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 1
J 2
14
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 1
J 2
15
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 1
J 2
16
A few steps later
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DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 1
J 6
18
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 1
J 6
19
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 1
J 6
20
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 2
J 6
21
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 2
J 6
22
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 2
J 6
23
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 2
J 1
24
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 2
J 1
25
A few steps later
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DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 3
J 6
27
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 4
J 6
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DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 4
J 6
29
DATA MEMORY

• 007 008 I 1009 IF I gt 3 GOTO 018010 J
  1 011 IF J gt 5 GOTO 015012 write()013
  J J 1014 GOTO 011015 writeln016 I I
  1017 GOTO 009018

I 4
J 6
30
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/icm
  is/oakman/outline/chap05/slides/symbols.htm

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Flowchart Symbols

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Rectangle Flow Chart
BEGIN
yes
I gt 3
no
yes
J gt 5
no
END
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Yes/No Choice

• The logic IF some condition or test is
  TRUE THEN 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 dont want to seem
  impolite, say hello back.

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Yes/No Choice The IF-THEN Statement

• Syntax IF ltconditiongt THEN ltstatementgt
• Syntax graph
• Flowchart

yes
condition
no
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Either/Or Choice

• The logic IF some condition or test is
  TRUE THEN perform some action ELSE 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.

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Either/Or Choice The IF-THEN-ELSE Statement

• Syntax IF ltconditiongt THEN ltstatementgt ELSE
  ltstatementgt
• Syntax graph
• Flowchart

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What is ltstatementgt ?

• 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 ltstatementgt ltstatementgt
  .ltstatementgt
• END

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What is ltconditiongt ?

• 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

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Boolean Expressions

• Boolean constants
• TRUE
• FALSE
• Boolean variables
• Declared as type boolean
• CONST
• Debug TRUE or FALSE
• VAR
• SaveDebug BOOLEAN

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• Relational expressions Arithmetic, character,
  or strings acted upon by relational operators
• Relational operators are
• lt less than or equal to
• lt less than
• gt greater than or equal to
• gt greater than
• equal
• ltgt not equal
• Relational operators compare two compatible
  values
• Two characters
• Two strings
• Real and integer
• Two Booleans
• Relational operators return a Boolean value

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• Examples
• new lt old
• B lt A
• value ltgt -99999
• 3.0 lt 4
• MiddleInitial L
• 1.0 1.0/ 3.0 3.0 Implementation
  dependent

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• 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
  bankELSE Ask parents for money
• IF Value lt MinValue OR Value gt MaxValue THEN
  writeln (Value , Value, is out of range.)

43
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
44
Operator Precedence Arithmetic, Relational and
Logical

• Operator Precedence
• ( ) parentheses Highest (evaluated first)
• - NOT (unary operators)
• / DIV MOD AND
• - OR
• lt lt ltgt gt gt Lowest (evaluated last)

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• (4.2 gt 5.0) AND (8 (3 5))
• (4.2 gt 5.0) OR (8 (3 5))
• writeln('Value of (-2 lt 0) AND (18 gt 10) is ',
• (-2 lt 0) AND (18 gt 10) )
• writeln('Value of (-2 lt 0) OR (18 gt 10) is
  ',
• (-2 lt 0) OR (18 gt 10) )
• writeln('Value of (3 gt 5) AND (14.1 0.0) is
  ',
• (3 gt 5) AND (14.1 0.0) )
• writeln('Value of (3 gt 5) OR (14.1 0.0) is
  ',
• (3 gt 5) OR (14.1 0.0) )
• writeln('Value of NOT (18 10 8) is ',
• NOT (18 10 8) )
• writeln('Value of NOT (-4 gt 0) is ',
• NOT (-4 gt 0) )
• writeln('Value of ''a'' lt ''b'' is ', 'a' lt
  'b' )
• writeln('Value of ''a'' lt ''A'' is ', 'a' lt
  'A' )

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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 cant read/readln a Boolean value)

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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
• var
• Debug, SaveDebug Boolean
• BEGIN
• SaveDebug Debug
• Debug TRUE
• IF Debug THEN
• print out the value of several variables
• Debug SaveDebug
• ...
• END

48
Example Expressions

• See program BOOLEXPR.PAS

49
Go Over Homework 2, Programming Part
50
Exercises 1.5, 13

• Write a complete program that produces the
  following table
• WIDTH LENGTH AREA
• 4 2 8
• 21 5 105

51
Task Decomposition (1)

• Write table header
• WIDTH LENGTH AREA
• Write table contents
• 4 2 8
• 21 5 105
• Simplest code
• writeln(WIDTH LENGTH AREA)
• writeln( 4 2 8)
• writeln( 21 5 105)

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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 284 14
• Third column fits in field of 284 14
• Code will be
• writeln(WIDTH, 8,LENGTH, 8,AREA)
• writeln(43,214,814)
• writeln(213,514,10514)

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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.

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Desired Output

• 12345678901234567890123456789012345678901234
• -------------------------
• Employees Hourly Wage
• -------------------------
• 1 3.65
• 2 4.10
• 3 2.89
• 4 5.00
• 5 4.50
• -------------------------

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Task Decomposition (1)

• Write table header
• -------------------------
• Employees Hourly Wage
• -------------------------
• Write table contents
• 1 3.65
• .
• Write table footer
• -------------------------

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

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

58
Task Decomposition (3)

• Write table header
• Write line starting at column 20
• Write column headings starting at column 20
• Write line starting at column 20
• -------------------------
• Employees Hourly Wage
• -------------------------
• Pascal code
• CONST Line -------------------------
• BEGIN
• writeln( 19,Line)
• writeln( 19,Employee, 5,Hourly
  Wage)
• writeln( 19,Line)
• END.

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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(123,13,3.6552)
• writeln(223,13,4.1052)
• writeln(323,13,2.8952)
• writeln(423,13,5.0052)
• writeln(523,13,4.5052)
• END.

60
Task Decomposition (5)

• Write table footer
• Write line starting at column 20
• -------------------------
• Pascal code
• CONST Line -------------------------
• BEGIN
• ...
• writeln( 19,Line)
• END.