Programming Lecture 5

8/3/2019 Programming Lecture 5

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Java Programming: From Problem

Analysis to Program Design, 3e

Chapter 5

Control Structures II: Repetition


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2Java 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 controlstructures


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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


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The while Looping (Repetition)

Structure Syntaxwhile (expression)

statement

Expression is always true in an infinite loop

Statements must change value of expression to

false


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Structure (continued)


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Structure (continued)Example 5-1

i = 0; //Line 1

while (i


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Structure (continued) Typically, while loops are written in the

following form:


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Counter-Controlled while Loop

Used when exact number of data or entry piecesis known

General form:


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Sentinel-Controlled while Loop

Used when exact number of entry pieces isunknown but last entry (special/sentinel value) isknown

General form:


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Flag-Controlled while Loop

Boolean value used to control loop

General form:


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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 usesthe Scanner object console to inputdata, console acts at the loop controlvariable

The method hasNext, of the classScanner, returns true if there is an inputin the input stream; otherwise it returnsfalse


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Java Programming: From Problem Analysis to Program Design, 3e

EOF(End of File)-Controlledwhile Loop (continued)

The expression console.hasNext() evaluatesto 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 inputdata is of the form:


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EOF(End of File)-Controlled

while Loop (continued) Suppose that inFile is a Scanner object

initialized to the input file; in this case, the EOF-controlled while loop takes the following form:


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Programming Example:

Checking Account Balance Input file: customers 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, totalamount deposited, number of deposits, totalamount withdrawn, number of withdrawals


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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)


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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 number2

int nthFibonacci = position of nth Fibonacci number

Output: nth Fibonacci number


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Programming Example: Fibonacci

Number (Solution)if (nthFibonacci == 1)

current = previous1;

else if (nthFibonacci == 2)

current = previous2;

else

{

counter = 3;

while (counter


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The for Looping (Repetition)

Structure Specialized form ofwhile loop

Simplifies the writing of count-controlled loops

Syntax:for (initial expression; logical expression;

update expression)

statement


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Structure (continued) Execution

Initial statement executes

The loop condition evaluated

If loop condition evaluates to true, executefor loop statement and execute updatestatement

Repeat until loop condition is false


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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();


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Structure (continued)Example 5-91. The following for loop outputs the word Hello and a star (on separate

lines) five times:

for (i = 1; i


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Structure (continued) Does not execute if initial condition isfalse

Update expression changes value of loopcontrol variable, eventually making it false

If logical expression is always true, resultis an infinite loop

Infinite loop can be specified by omitting allthree control statements


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If logical expression is omitted, it isassumed to be true

for statement ending in semicolon isempty

Java Programming: From Problem Analysis to Program Design, 3e24


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Programming Example: Classify

Numbers Input: N integers (positive, negative, and zeros)

int N = 20; //N easily modified

Output: number of0s, number of even integers,

number of odd integers


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Programming Example: Classify

Numbers (Solution)for (counter = 1; counter


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The dowhile Loop

(Repetition) Structure Syntax:

Statements executed first, then logical

expression evaluated Statement(s) executed at least once then

continued iflogical expression is true


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dowhile Loop (Post-test Loop)


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breakStatements

Used to exit early from a loop

Used to skip remainder ofswitch

structure

Can be placed within if statement of a loop

If condition is met, loop exited immediately


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continue Statements

Used in while, for, and do...whilestructures

When executed in a loop, the remaining

statements in the loop are skipped; proceedswith the next iteration of the loop

When executed in a while/dowhilestructure, expression evaluated immediately

aftercontinue statement In a for structure, the update expression isexecuted after the continue statement;then the loop condition executes


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Nested Control Structures Provides new power, subtlety, and

complexity

if, ifelse, and switch structures can

be placed within while loops

for loops can be found within otherfor

loops


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Nested Control Structures (Example)

for (int i = 1; i


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Chapter Summary

Looping Mechanisms Counter-controlled while loop

Sentinel-controlled while loop

Flag-controlled while loop EOF-controlled while loop

for loop

dowhile loop

break statements continue statements

Nested control structures

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Programming Lecture 5