Download Chapter 5

JAVA PROGRAMMING: FROM
PROBLEM ANALYSIS TO PROGRAM
DESIGN, 3E
Control Structures II: Repetition
CHAPTER 5
Java Programming: From Problem Analysis to
Program Design, 3e
CHAPTER OBJECTIVES




Learn about repetition (looping) control structures
Explore how to construct and use count-controlled,
sentinel-controlled, flag-controlled, and EOF-controlled
repetition structures
Examine break and continue statements
Discover how to form and use nested control
structures
2
Java Programming: From Problem Analysis to
Program Design, 3e
WHY IS REPETITION NEEDED?
There are many situations in which the same
statements need to be executed several times
 Example

 Formulas
used to find average grades for students
in a class
3
Java Programming: From Problem Analysis to
Program Design, 3e
THE WHILE LOOPING (REPETITION)
STRUCTURE

Syntax
while (expression)
statement


Expression is always true in an infinite loop
Statements must change value of expression to false
4
Java Programming: From Problem Analysis to
Program Design, 3e
THE WHILE LOOPING (REPETITION)
STRUCTURE (CONTINUED)
5
Java Programming: From Problem Analysis to
Program Design, 3e
THE WHILE LOOPING (REPETITION)
STRUCTURE (CONTINUED)
Example 5-1
i = 0;
while (i <= 20)
{
System.out.print(i + " ");
i = i + 5;
}
System.out.println();
//Line 1
//Line 2
//Line 3
//Line 4
//Line 5
Output:
0 5 10 15 20
6
Java Programming: From Problem Analysis to
Program Design, 3e
THE WHILE LOOPING (REPETITION)
STRUCTURE (CONTINUED)

Typically, while loops are written in the
following form:
7
Java Programming: From Problem Analysis to
Program Design, 3e
COUNTER-CONTROLLED WHILE LOOP
Used when exact number of data or entry
pieces is known
 General form:

8
Java Programming: From Problem Analysis to
Program Design, 3e
SENTINEL-CONTROLLED WHILE LOOP
Used when exact number of entry pieces is
unknown but last entry (special/sentinel value)
is known
 General form:

9
Java Programming: From Problem Analysis to
Program Design, 3e
FLAG-CONTROLLED WHILE LOOP
Boolean value used to control loop
 General form:

10
Java Programming: From Problem Analysis to
Program Design, 3e
EOF(END OF FILE)-CONTROLLED WHILE LOOP
Used when input is from files
 Sentinel value is not always appropriate
 In an EOF-controlled while loop that
uses the Scanner object console to
input data, console acts at the loop
control variable
 The method hasNext, of the class
Scanner, returns true if there is an
input in the input stream; otherwise it
returns false

11
EOF(END OF FILE)-CONTROLLED
WHILE LOOP (CONTINUED)
Java Programming: From Problem Analysis to
Program Design, 3e
The expression console.hasNext()
evaluates to true if there is an input in the input
stream; otherwise it returns false
 Expressions such as console.nextInt() act
as the loop condition
 A general form of the EOF-controlled while loop
that uses the Scanner object console to input
data is of the form:

12
Java Programming: From Problem Analysis to
Program Design, 3e
EOF(END OF FILE)-CONTROLLED
WHILE LOOP (CONTINUED)

Suppose that inFile is a Scanner object
initialized to the input file; in this case, the EOFcontrolled while loop takes the following form:
13
Java Programming: From Problem Analysis to
Program Design, 3e
PROGRAMMING EXAMPLE: CHECKING
ACCOUNT BALANCE
Input file: customer’s account number, account
balance at beginning of month, transaction
type (withdrawal, deposit, interest), transaction
amount
 Output: account number, beginning balance,
ending balance, total interest paid, total
amount deposited, number of deposits, total
amount withdrawn, number of withdrawals

14
Java Programming: From Problem Analysis to
Program Design, 3e
PROGRAMMING EXAMPLE: CHECKING
ACCOUNT BALANCE (CONTINUED)

Solution
 Read
data
 EOF-controlled loop
 switch structure of transaction types
 Determine
action (add to balance or subtract from
balance depending on transaction type)
15
Java Programming: From Problem Analysis to
Program Design, 3e
PROGRAMMING EXAMPLE: FIBONACCI
NUMBER

Fibonacci formula for any Fibonacci sequence:
an = an-1 + an-2

Input: first two Fibonacci numbers in sequence,
position in sequence of desired Fibonacci
number (n)




int previous1 = Fibonacci number 1
int previous2 = Fibonacci number 2
int nthFibonacci = position of nth Fibonacci number
Output: nth Fibonacci number
16
PROGRAMMING EXAMPLE: FIBONACCI
NUMBER (SOLUTION)
Java Programming: From Problem Analysis to
Program Design, 3e
if (nthFibonacci == 1)
current = previous1;
else if (nthFibonacci == 2)
current = previous2;
else
{
counter = 3;
while (counter <= nthFibonacci)
{
current = previous2 + previous1;
previous1 = previous2;
previous2 = current;
counter++;
}
}

Final result found in last value of current
17
Java Programming: From Problem Analysis to
Program Design, 3e
THE FOR LOOPING (REPETITION)
STRUCTURE

Specialized form of while loop
Simplifies the writing of count-controlled loops
 Syntax:

for (initial expression; logical expression;
update expression)
statement
18
Java Programming: From Problem Analysis to
Program Design, 3e
THE FOR LOOPING (REPETITION)
STRUCTURE (CONTINUED)

Execution
 Initial
statement executes
 The loop condition evaluated
 If loop condition evaluates to true,
execute for loop statement and execute
update statement
 Repeat until loop condition is false
19
Java Programming: From Problem Analysis to
Program Design, 3e
THE FOR LOOPING (REPETITION)
STRUCTURE (CONTINUED)
20
Java Programming: From Problem Analysis to
Program Design, 3e
THE FOR LOOPING (REPETITION)
STRUCTURE (CONTINUED)
Example 5-8
The following for loop prints the first 10
nonnegative integers:
for (i = 0; i < 10; i++)
System.out.print(i + " ");
System.out.println();
21
THE FOR LOOPING (REPETITION)
STRUCTURE (CONTINUED)
Java Programming: From Problem Analysis to
Program Design, 3e
Example 5-9
1.
The following for loop outputs the word Hello and a star (on separate
lines) five times:
for (i = 1; i <= 5; i++)
{
System.out.println("Hello");
System.out.println("*");
}
2.
for (i = 1; i <= 5; i++)
System.out.println("Hello");
System.out.println("*");
This loop outputs the word Hello five times and the star only once
22
Java Programming: From Problem Analysis to
Program Design, 3e
THE FOR LOOPING (REPETITION)
STRUCTURE (CONTINUED)
Does not execute if initial condition is
false
 Update expression changes value of loop
control variable, eventually making it
false
 If logical expression is always true, result
is an infinite loop
 Infinite loop can be specified by omitting all
three control statements

23
Java Programming: From Problem Analysis
to Program Design, 3e
THE FOR LOOPING (REPETITION)
STRUCTURE (CONTINUED)
If logical expression is omitted, it is
assumed to be true
 for statement ending in semicolon is
empty

24
Java Programming: From Problem Analysis to
Program Design, 3e
PROGRAMMING EXAMPLE: CLASSIFY
NUMBERS

Input: N integers (positive, negative, and
zeros)
int N = 20;

//N easily modified
Output: number of 0s, number of even
integers, number of odd integers
25
PROGRAMMING EXAMPLE: CLASSIFY
NUMBERS (SOLUTION)
Java Programming: From Problem Analysis to
Program Design, 3e
for (counter = 1; counter <= N; counter++)
{
number = console.nextInt();
System.out.print(number + " ");
switch (number % 2)
{
case 0:
evens++;
if (number == 0)
zeros++;
break;
case 1:
case -1:
odds++;
} //end switch
} //end for loop
26
Java Programming: From Problem Analysis to
Program Design, 3e
THE DO…WHILE LOOP (REPETITION)
STRUCTURE

Syntax:

Statements executed first, then logical
expression evaluated

Statement(s) executed at least once then
continued if logical expression is true
27
Java Programming: From Problem Analysis
to Program Design, 3e
DO…WHILE LOOP (POST-TEST LOOP)
28
Java Programming: From Problem Analysis to
Program Design, 3e
BREAK STATEMENTS
Used to exit early from a loop
 Used to skip remainder of switch structure
 Can be placed within if statement of a loop

 If
condition is met, loop exited immediately
29
Java Programming: From Problem Analysis to
Program Design, 3e
CONTINUE STATEMENTS
Used in while, for, and do...while
structures
 When executed in a loop, the remaining
statements in the loop are skipped;
proceeds with the next iteration of the
loop
 When executed in a while/do…while
structure, expression evaluated
immediately after continue statement
 In a for structure, the update expression
is executed after the continue
statement; then the loop condition
executes

30
Java Programming: From Problem Analysis to
Program Design, 3e
NESTED CONTROL STRUCTURES
Provides new power, subtlety, and complexity
 if, if…else, and switch structures can be
placed within while loops
 for loops can be found within other for loops

31
Java Programming: From Problem Analysis to
Program Design, 3e
NESTED CONTROL STRUCTURES (EXAMPLE)
for (int i = 1; i <= 5; i++)
{
for (int j = 1; j <= i; j++)
System.out.print(" *");
System.out.println();
}

Output:
*
**
***
****
*****
32
Java Programming: From Problem Analysis to
Program Design, 3e
CHAPTER SUMMARY

Looping Mechanisms






Counter-controlled while loop
Sentinel-controlled while loop
Flag-controlled while loop
EOF-controlled while loop
for loop
do…while loop
break statements
 continue statements
 Nested control structures

33