Chapter 5: Control Structure Part 2

1
Chapter 5 Control Structure
Part 2

• Presented by Tuong-Uyen Nguyen

2
Objectives

• 5.1 Introduction
• 5.2 Essentials of Counter-Controlled Repetition
• 5.3 The for Repetition Structure
• 5.4 Example Using the for Structure
• 5.5 The Multiple-Selection Structure
• 5.6 The do/while Repetition Structure
• 5.7 The break and continue Statements
• 5.8 The Labeled break and continue Statements
• 5.9 Logical Operators
• 5.10 Structured Programming Summary

3
5.1 Introduction

• Before writing a program to solve a particular
  problem
• - Understand the problem.
• - Plan approach to solving the
  problem.
• When writing a program
• - Understand the types of building
  blocks
• that are available and to employ
  proven
• program construction principles.

4
5.2 Essentials of Counter- Controlled
Repetition

• Counter-controlled repetition requires
• 1. The name of control variable (or loop
  counter).
• 2. The initial value of the control variable.
• 3. The increment (or decrement) by which the
• control variable is modified each time
  through
• the loop.
• 4. The condition that tests for the final
  value of the
• control variable.

5
5.2 (cont)

• Simple applet shown in Fig. 5.1 / page 159

6
5.2 (cont)

• int counter 1
• names the control variable (counter),
• declares it to be an integer.
• initial value of 1.
• int counter // declare counter
• counter 1 // initialize counter to
  1
• Line 12 in the while structure
• g.drawLine( 10, 10, 250, counter 10 )
• Graphics reference g, which refers to the
  applets Graphics object, to send the drawLine
  message to the Graphics object asking it to draw
  a line.

7
5.2 (cont)

• Line 13 in the while structure
• counter //increment
• increments the control variable by 1 each
  iteration of the loop.
• The program in Fig. 5.1 can be more concise by
  initializing counter to 0
• while ( counter lt 10 ) //repetition
  condition
• g.drawLine( 10, 10, 250, counter 10 )
  

8
5.3 The for Repetition Structure

• The for repetition structure handles all the
  details of counter-controlled repetition.

9
5.3 (cont)

• The applets paint method operates as follows
• When the for structure (line 11) begins
  executing, the control variable counter is
  initialized to 1.
• Next, the loop-continuation condition counterlt10
• is checked. The condition contains the
  final value(10) of the control variable.
• Because the initial value of counter is 1, the
  condition is satisfied, so the body statement
  (line 12) draws a line.

10
5.3 (cont)

• Variable counter is then incremented in the
  expression counter, the loop begins again with
  the loop-continuation test.
• This process continues until the control variable
  counter is incremented to 11, this causes the
  loop-continuation test to fail and repetition
  terminates.
• The program continues by performing the first
  statement after the for structure.

11
5.3 (cont)

• for key word control variable name
  Final value of control variable
• for ( int counter 1 counter lt
  10 counter )
• Initial value of control variable
  Increment control variable
• 
  Loop-continuation condition
• is called the for structure header. If there
  is
• more than one statement in the body of the for
• Braces ( and ) are required to define the
  body of the loop.

12
5.3 (cont)

• An off-by-one error
• Instead of coding counter lt 10, writing
• counter lt 10, the
  loop would be only executed nine times.
• The general format of the for structure
• for ( expression1 expression2
  expression3 )
• statement

13
5.3 (cont)

• expression1 names the loops control variable and
  provides its initial value.
• expression2 is the loop-continuation condition.
• expression3 increments the control variable.
• An equivalent while structure
• expression1
• while ( expression2 )
• statement
• expression

14
5.4 Examples Using the for Structure

• Fig. 5.4 Flowcharting a typical for repetition
  structure.

15
5.4 (cont)

• 1. Vary the control variable from 1 to 100 in
  increments of 1.
• for ( int I 1 i lt 100 i )
• 2. Vary the control variable form 100 to 1 in
  increments of 1 (decrements of 1).
• for ( int i 100 i gt 1 i-- )
• 3. Vary the control variable from 20 to 2 in
  steps of 2
• for ( int i 20 i gt 2 i -
  2 )

16
Fig. 5.5 Summation with for (even integer
from 2-100)
17
Fig. 5.6 Calculating compound
interest with for
18
5.5 The switch Multiple-Selection
Structure

• The switch multiple-selection structure contains
  a series of decisions in which a variable or
  expression is tested separately for each of the
  constant integral values.

19
Fig. 5.7 An Example Using switch
20
5.5 (cont)

• 7 int choice
• Line 7 in applet SwitchTest defines instance
  variable choice of type int.
• 9 public void init( )
• Line 9 init declares local variable input of
  type String at line 11.
• 13 input
  JOptionPane.showInputDialog(
• 14
  Enter 1 to draw lines n
• 15
  Enter 2 to draw rectangles n
• 16
  Enter 3 to draw ovals n )
• Lines 13-16 display the input dialog with static
  method JOptionPane.showInputDialog

21
Fig. 5.8 The switch multiple-
selection structure
22
5.6 The do/while Repetition
Structure

• Tests the loop-continuation condition after
• the loop body is performed.
• The loop body is always executed once.
• When a do/while terminates, execution continues
  with the statement after the while
• statement
• clause.
• do
• while ( condition )

23
Fig. 5.9 Using the do/while
Repetition Structure
24
Fig. 5.10 Flowchart the do/while
Repetition Structure
action(s)
true
condition
false
25
5.7 The break and continue Statements

• The break statement, when executed in a while,
  for, do/while or switch structure, causes
  immediate exit from that structure.
• The breaks common use is to escape early from
  the loop or to skip the remainder of a switch
  structure.
• The continue statement, when executed in a while,
  for or do/while structure, skips the remaining
  statement in the body, and proceeds with the next
  iteration of the loop.

26
Fig. 5.11 Using the break statement
in a for structure
27
Fig. 5.12 Using the continue statement
in a for structure
28
5.8 The Labeled break and continue
Statements

• To break out of a nested set of structures.
• Commonly used to terminate nested looping
  structures containing while, for, do/while or
  switch structure.

29
Fig. 5.13 Using a labeled break statement
in a nested for structure
30
5.9 Logical Operators

• (logical AND) gender 1 age gt 65
• (boolean logical AND)
• // (logical OR) semesterAverage gt 90 //
  finalExam gt 90
• / ( boolean logical inclusive OR)
• (boolean logical exclusive OR)
• ! (logical NOT)

31
Truth Tables of 4 Operators
32
Fig. 5.14 Using labeled continue statement in
a nested for structure
33
5.10 Structured Programming Summary

• Three forms of control are needed
• 1. Sequence
• 2. Selection
• 3. Repetition
• Sequence is trivial. Selection is implemented in
  3 ways
• 1. if structure (single selection)
• 2. if/else structure ( double selection)
• 3. switch structure ( multiple selection)
• Repetition is implemented in 3 ways
• 1. while structure
• 2. do/while structure
• 3. for structure

34
Fig. 5.21 on page 188
35
QUESTIONS???
Web-Site
http//students.ou.edu/N/Tuong-Uyen.P.Nguyen-1/MIS
3033
The End.