MSI 692: Special Topics in Information Technology

1

• MSI 692 Special Topics in Information Technology
• Lecture 2
• Sanjay Goel
• University at Albany, SUNY
• Fall 2004

2
Outline for the ClassTopics

• Review
• Statements and Control Flow
• Boolean Expressions
• Logical Operators
• Logical Statements
• if, else if, nesting, switch
• Loops (while, for, break)
• Object-oriented Programming

3
Statements and Control Flow
4
Statements and Control FlowIntroduction

• We have learned how to write words in a language.
  
• We need to learn how to make sentences and
  paragraphs now.
• What do you need to do when you are doing a
  complex problem?
• You have certain process to follow you have
  decision points where you use your mind to make
  decisions.
• To build your own logic into a computer program
  you need to write statements that capture your
  logic.
• How to introduce logic into the program?

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Statements and Control FlowStatements

• Statements are roughly equivalent to sentences in
  natural languages.
• A statement forms a complete unit of execution.
• It has many different types
• Variable Declaration Statement
• Expression Statement
• Assignment Statement
• Method Call Statement
• Control Flow Statement

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Statements and Control Flow Variable declaration
statements

• Variable declaration statements are used to
  identify the type of the variable that is being
  declared
• start with a type and end with a semicolon
• e.g.
• int width, height, area
• String myString

7
Statements and Control FlowExpressions

• An expression is a series of variables,
  operators, and method calls (constructed
  according to the syntax of the language) that
  evaluates to a single value.
• Also defined as segments of code that perform
  computations and return values.
• Data type of the value returned by an expression
  depends on the elements used in the expression.
• Compound expressions and statements can be
  constructed from various smaller expressions as
  long as the data types required by one part of
  the expression matches the data types of the
  other.
• If the order in which the operations in a
  compound expression need to be performed is not
  explicitly indicated, the order is determined by
  the precedence assigned to the operators

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Statements and Control FlowExpression Statements

• Expression statements are formed by adding a
  semicolon at end of expression.
• These are used to compute and to assign values to
  variables and to help control the execution flow
  of a program.
• The following types of expressions can be made
  into a statement by terminating the expression
  with a semicolon ()
• Assignment expressions
• Any use of or
• Method calls
• Object creation expressions
• Examples
• aValue 8933.234 //assignment statement
• aValue //increment statement
• System.out.println(aValue) //method call
  statement
• Integer integerObject new Integer(4) //object
  creation statement

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Statements and Control FlowAssignment Statements

• Assignment statement can be any expression
  involving the assignment operator.
• e.g. area length width
• Method Call Statement invokes other functions
• Method call expression involves assignment when
  the method returns a statement.
• e.g. System.out.println(This is a test)

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Statements and Control FlowBlocks

• Block is a group of statements enclosed in
  braces.
• Blocks can occur within blocks and are called
  nested blocks
• e.g.
• float length 2
• float width 2
• float area length width
• System.out.println(area area) 
• Empty or Null Statement
• It is just a semicolon all by itself and results
  in no action.
• e.g. Consider the following program lines 2
  3 are null statement
• x 2 ? Line 1
• ? Line 2
• ? Line 3

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Boolean Logical Expressions
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Boolean ExpressionsIntroduction

• These are expressions which evaluate to true or
  false.
• The simplest Boolean expressions are true and
  false
• All conditional statements require Boolean
  expressions to decide flow of logic

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Boolean ExpressionsRelational Equality
Operators

• Relational Equality Operators
• used for comparing numeric values
• lt gt lt gt !
• These operators can be used between any two
  numeric values, e.g.
• int a 10
• int b 20
• int c 15
• a gt b ? false
• a lt b ? true
• c lt 10 ? false

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Logical ExpressionsOperators

• These are used for combining multiple logical
  statements
• Three logical operators
• - and
• ! - not
• - or
• Examples (See next page)

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Boolean Logical ExpressionsExercises

• Assume the following
• int i, j, k boolean b k 10 j 6 b true
• Give the values of the following expressions, or
  state if illegal.
• b
• !b
• !!!!!!b
• b !b
• b !b
• b true
• b
• b 1
• b 1 gt 2
• true 1234/2631
• true 1234/2631

• !b (j lt 100)
• k gt j gt 3
• k gt j gt 3
• k gt j k gt 3
• b false
• b false
• k (kgtj)?kj1
• (b !b) (!b b)
• 1 gt 2 gt 3
• b j gt 0 (i k/j)!0

Source http//leepoint.net/notes-java/20language/
20expressions/60booleanex.html
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Boolean ExpressionsExercises - Solutions

• 1 true b
• 2 false !b
• 3 true !!!!!!b
• 4 true b !b
• 5 false b !b
• 6 false b true
• 7 illegal b
• 8 illegal b 1
• 9 false b 1 gt 2
• 10 true true 1234/2631
• 11 true true 1234/2631
• 12 false !b (j lt 100)
• 13 illegal k gt j gt 3
• 14 illegal k gt j gt 3

15 true k gt j k gt 3 16 illegal b
false 17 true b false 18 10 k
(kgtj)?kj1 19 false (b !b) (!b
b) 20 illegal 1 gt 2 gt 3 21 true b j gt 0 (i
k/j)!0
Source http//leepoint.net/notes-java/20language/
20expressions/60booleanex.html
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Logical Statements
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Logical StatementsIf Statement

• If statement is a conditional statement which
  proceeds based on the evaluation of an
  expression, e.g.
• if ( temp lt 32)
• System.out.println(It is below freezing
  today)
• System.out.println(Temperature temp) 
• For multiple statements depending on a
  conditional we use blocks, e.g.
• if (temp lt 32)
• System.out.println(It is below freezing)
• System.out.println(Keep all the windows
  closed)

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Logical StatementsSorting Algorithm

• Example to sort three numbers

• / Bubble Sort Algorithm. In this
• algorithm the smallest number
• /bubbles to the top
• public static void main(String args)
• int a Console.in.readInt()
• int b Console.in.readInt()
• int c Console.in.readInt()
• int t // Temporary variable
• if (a gt b)
• // Swap a and b
• t a
• a b
• b t

if (b gt c) // swap b c t b b c c
t if (a gt b) // Swap a b t a a
b b t System.out.println(The sorted
numbers are a b c)
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Logical StatementsIf else Statement

• If else statement is a bi-directional logic
  expression
• Syntax
• if (Boolean expression)
• Statement1
• else
• Statement2
• Example
• if (temp lt 32)
• System.out.println(Close all the windows)
• else
• System.out.println(Open all the windows) 

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Logical StatementsNesting

• Nesting is allowed within if and if else
  statements
• if (temp lt 32)
• System.out.println(Below Freezing)
• if (temp lt 20)
• System.out.println(School is off)
• else
• System.out.println(Go To School)
• else
• if (temp gt 70)
• System.out.println(Go to the beach)
• else
• System.out.println(Go to school)

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Logical StatementsDangling Else

• else goes with the closest if statement
• if (temp lt 32)
• if (temp lt 20)
• System.out.println(Stay indoors)
• else
• System.out.println(Keep Warm)
• Here the else statement goes with the second if
  statement

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Logical StatementsSwitch

• Switch statement conditionally executes
  statements based on an integer expression
• it is a multidirectional logic statement that
  can replace multiple if statements

• If (day 1) System.out.println(Sunday)
• If (day 2) System.out.println(Monday)
• If (day 3) System.out.println(Tuesday)
• If (day 4) System.out.println(Wednesday)
• If (day 5)System.out.println(Thursday)
• If (day 6) System.out.println(Friday)
• If (day 7) System.out.println(Saturday)

switch (day) case 1 System.out.println(S
unday) break case 2
System.out.println(Monday) break case
3 System.out.println(Tuesday)
break case 4 System.out.println(Wednesday
) break case 5 System.out.println(Th
ursday) break case 6
System.out.println(Friday) break case
7 System.out.println(Saturday)
break default System.out.println(Illegal
Value day)
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Logical StatementsWhile

• While statement is used to continually execute a
  block of statements while a condition remains
  true.
• Syntax
• while (expression) statement
• Operation
• First, the while statement evaluates expression,
  which must return a boolean value.
• If the expression returns true, then the while
  statement executes the statement(s) associated
  with it.
• The while statement continues testing the
  expression and executing its block until the
  expression returns false.
• int i 0
• while (i lt 100)
• System.out.println(i)
• i

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Logical Statementsdo-while

• do-while is similar to while statement that
  instead of evaluating the expression at the top
  of the loop, evaluates the expression at the
  bottom.
• Statements associated with a do-while are
  executed at least once
• Syntax
• do statement(s) while (expression)
• Operation
• First the do statement executes the statement(s)
  associated with it.
• Then the while statement evaluates expression
  that must return a boolean.
• The do statement continues executing its block
  and the while statement continues testing the
  expression until the expression returns false.
• Example
• int i 0
• do
• System.out.println(i)
• i
• while (i lt 100)

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Logical StatementsFor

• for statement provides a compact way to iterate
  over a range of values.
• Syntax
• for (initialization termination increment)
  statement
• The initialization is an expression that
  initializes the loop-it's executed once at the
  beginning of the loop.
• The termination expression determines when to
  terminate the loop. This expression is evaluated
  at the top of each iteration of the loop. When
  the expression evaluates to false, the loop
  terminates.
• Finally, increment is an expression that gets
  invoked after each iteration through the loop.
• e.g. Example
• for (int i 0 i lt 10 i)
• System.out.println(My value is i)

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Logical StatementsBreak

• Break causes an exit from the innermost enclosing
  loop.
• Break statements in loops should usually be
  avoided as they alter the flow of control
  associated with loop statements
• from a clear "in at the top" to "out at the
  bottom" to something which is less obvious.
• A break statement can sometimes be used
  "legitimately" to "break out" of a continuous
  loop.
• However, in most cases there is an alternative
  strategy that will avoid the use of a break.
• Continue causes the current iteration of the
  program to stop and the next to continue.
• e.g.
• for (int i0 ilt100 i)
• System.out.println( Square of i
  ii)
• if (ii gt 10000) break

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Logical StatementsContinue

• A continue statement returns to the beginning of
  the innermost enclosing loop without completing
  the rest of the statements in the body of the
  loop (for, while and do-while).
• If you're in a for loop, the counter is
  incremented.
• Rarely used in practice
• e.g.
• for (int i 0 i lt m.length i)
• if (mi 2 0) continue // process odd
  elements...
• System.out.println(Square of i
  ii)

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Recap
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RecapStatements

• Statements are roughly equivalent to sentences in
  natural languages.
• A statement forms a complete unit of execution.
• It has many different types
• Variable Declaration Statement
• Expression Statement
• Assignment Statement
• Method Call Statement
• Control Flow Statement
• Variable declaration statements are used to
  identify the type of the variable that is being
  declared
• These statements start with a type and end with a
  semicolon

31
RecapExpression Statements

• Expression is a series of variables, operators,
  and method calls (constructed according to the
  syntax of the language) that evaluates to a
  single value.
• Expression Statements are formed by adding a
  semicolon at end of expression.
• Assignment statement
• Any expression involving the assignment operator.
• e.g. area length width
• Method Call Statement
• Method call expression does not involve
  assignment.
• e.g. System.out.println(This is a test)

32
RecapBlocks and Empty/Null Statements

• Block is a group of statements enclosed in
  braces. Blocks can occur within blocks and are
  called nested blocks
• e.g.
• float length 2
• float width 2
• float area length width
• System.out.println(area area) 
• Empty or Null Statement It is just a semicolon
  all by itself and results in no action.
• e.g. x 2

33
RecapRelational Equality Operators

• Boolean Expressions
• Evaluate to true or false
• All conditional statements require Boolean
  expressions to decide flow of logic
• Relational Equality Operators
• used for comparing numeric values
• lt gt lt gt !
• These operators can be used between any two
  numeric values, e.g.
• int a 10
• int b 20
• int c 15
• a gt b ? false
• a lt b ? true
• c lt 10 ? false

34
RecapLogical Operators

• These are used for combining multiple logical
  statements
• Three logical operators
• - and
• ! - not
• - or

35
RecapLogical Statements

• if statement
• conditional statement which proceeds based on the
  evaluation of an expression  
• if (boolean-expression) then statement
• if-else statement
• bi-directional logic expression
• if (boolean expression) Statement11 else
  Statement2
• Nesting of if and if else statements
• Allows complex logic to be modeled
• Dangling else
• else goes with the closest if statement

36
RecapSwitch Statement

• Switch is a multidirectional logic statement.
• Switch(op)
• case a statementa
• break
• case b statementb
• break
• default
• statement
• Notes
• Only one default statement in the switch
• Case and Default cannot occur outside of the
  switch
• break exits the switch statement
• Without break execution falls to next statement
  in the succeeding case
• By not using break, you can combine multiple
  cases

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RecapLoops or iterations

• while Statement
• while (expression) statement
• do-while is similar to while where expression
  evaluated at bottom.
• do statement(s) while (expression)
• for Statement
• for(init statement termination expression
  increment statement)
• block of statements
• break and continue
• break causes an exit from the innermost
  enclosing loop.
• continue causes the current iteration of the
  program to stop and the next to continue.