Upload File

loop variations do-while and for loops. do-while loops slight variation of while loops instead of...

  • Home
  • Documents
  • Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop
30
Loop variations do-while and for loops

Post on 20-Dec-2015

249 views

Category:

Documents


2 download

Report

TRANSCRIPT

Page 1: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Loop variations

do-while and for loops

Page 2: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Do-while loops

• Slight variation of while loops• Instead of testing condition, then

performing loop body, the loop body is performed first, then condition is tested

• A do-while loop is guaranteed to perform one iteration, because the validity of the condition is not known until after the iteration is complete

Page 3: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Syntax for do-while loop

do {/* loop body statements */

}while (expression);

Notes:• do-while loops are almost always event-controlled• Often not necessary to initialize loop control• Good idea to keep end bracket and while(expression) on same line

Page 4: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

do {

sum += number;

number++;

} while ( sum <= 1000000 );

Syntax for the do-while Statementdo

<statement>

while ( <boolean expression> ) ;

Statement(loop body)

Statement(loop body)

Boolean ExpressionBoolean Expression

Page 5: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Control Flow of do-while

int sum = 0, number = 1int sum = 0, number = 1

sum += number;

number++;

sum += number;

number++;

sum <= 1000000 ?

sum <= 1000000 ?

true

false

Page 6: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Applications for do-while loops

• Often used to display an initial menu of choices, one of which is “quit program” – you want user to see this at least once, even if the option they pick is to quit

• Useful for checking validity of input value – eliminates having to prompt twice for same data (see examples, next two slides)

Page 7: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Validating input – while loop

Scanner kb = new Scanner(System.in);int x;System.out.print(“Enter a number between 1 and 100: ”);x = kb.nextInt();while(x < 1 || x > 100) {

System.out.println(“Value out of range”);System.out.print(“Enter a number between 1 and 100: ”);x = kb.nextInt();

}

Page 8: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Validating input – do-while loop

Scanner kb = new Scanner(System.in);int x;

do {System.out.print(“Enter a number between 1 and 100: ”);x = kb.nextInt();if (x < 1 || x > 100)

System.out.println(“Value out of range”);} while(x < 1 || x > 100);

Page 9: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Do-While Loop vs. While Loop

• POST-TEST loop (exit-condition)

• The looping condition is tested after executing the loop body.

• Loop body is always executed at least once.

• PRE-TEST loop (entry-condition)

• The looping condition is tested before executing the loop body.

• Loop body may not be executed at all.

Page 10: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Confirmation Dialog• A confirmation dialog can be used to prompt the user

to determine whether to continue a repetition or not.

JOptionPane.showConfirmDialog(null,

/*prompt*/ "Play Another Game?",

/*dialog title*/ "Confirmation",

/*button options*/ JOptionPane.YES_NO_OPTION);

Page 11: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Example: Confirmation Dialog

boolean keepPlaying = true;

int selection;

while (keepPlaying) {

//code to play one game comes here

// . . .

selection = JOptionPane.showConfirmDialog(null,

"Play Another Game?",

"Confirmation",

JOptionPane.YES_NO_OPTION);

keepPlaying = (selection == JOptionPane.YES_OPTION);

}

Page 12: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Example: Confirmation Dialog

int selection;

do {

//code to play one game comes here

// . . .

selection = JOptionPane.showConfirmDialog(null,

"Play Another Game?",

"Confirmation",

JOptionPane.YES_NO_OPTION);

} while (selection == JOptionPane.YES_OPTION);

Page 13: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

For loops

• Count-controlled loops are so common in programming that most languages have a special set of syntax designed specifically for this construct

• In Java, the special syntax for a count-controlled loop is called a for loopfor loop

Page 14: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Count-controlled loops

• Count-controlled while loop:– initialize counter before loop starts– test counter in loop control expression– update counter inside loop body

• A for loop is a stylized version of a count-controlled while loop; all of the elements above appear at the top of the loop

Page 15: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

For Loop Syntax

for ( initialization ; test expression ; update ) {

0 or more statements to repeat

}

Page 16: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Control Flow of for

i = 0;i = 0;

false

number = . . . ;sum += number;

number = . . . ;sum += number;

true

i ++;i ++;

i < 20 ? i < 20 ?

Page 17: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

The for loop contains

an initialization

an expression to test for continuing

an update to execute after each iteration of the body

Page 18: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Count-controlled while loop example

int x=0; /* step 1: initialize counter */

while (x < 100) /* step 2: test counter value */{

System.out.println(“I will be a good student”);x++; /* step 3: increment counter */

}

Page 19: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Same logic using for loop

for (int x=0; x<100; x++) System.out.println(“I will be a good student”);

Step 1: initialize loop counter (performed once)

Step 2: test counter value (performed once for each iteration)

Step 3: increment loop counter (performed once per iteration)

Body of loop is performed between steps 2 and 3, just as in thewhile loop version

Page 20: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Notes on for loop

• Just stylized version of while loop; condition test occurs before each iteration

• Can contain single statement (making brackets unnecessary) because increment occurs in loop heading

• Each section of loop heading can contain multiple parts, separated by commas; each section can also be omitted

Page 21: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

for (int count = 4 ; count > 0 ; count-- )

{

System.out.println(“” + count);

}

System.out.println(“Done”);

Example using decrement

OUTPUT: 4321Done

Page 22: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Write a loop to producethe following output:

1Potato2Potato3Potato45Potato6Potato7PotatoMore

Page 23: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

What is output?

int count=0;

for (; count < 10 ; count++ )

{

System.out.println(“”);

}

Page 24: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

What is output?

int count=0;

for (; count < 10 ; count++ );

{

System.out.println(“*”);

}

Page 25: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

More for Loop Examplesfor (int i = 0; i < 100; i += 5)11

i = 0, 5, 10, … , 95 i = 0, 5, 10, … , 95

for (int j = 2; j < 40; j *= 2)22

j = 2, 4, 8, 16, 32 j = 2, 4, 8, 16, 32

for (int k = 100; k > 0; k--) )33

k = 100, 99, 98, 97, ..., 1k = 100, 99, 98, 97, ..., 1

Page 26: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Example – multiplication table

The loop displays a specified multiplication table. For example, if the user enters 6, the program displays this table:

1 x 6 = 6 2 x 6 = 12 3 x 6 = 18

.

.

.

12 x 6 = 72

Page 27: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

import java.util.*;

public class Mtable {public static void main(String [] args) {int value;Scanner kb = new Scanner(System.in);System.out.print (“Enter value for table: ”);value = kb.nextInt();for (int ct = 1; ct <= 12; ct++)

System.out.println( “” + ct + “ x ” + value+ “ = ” + ct * value);

}}

Page 28: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Loop-and-a-Half Repetition Control

• Loop-and-a-half repetition control can be used to test a loop’s terminating condition in the middle of the loop body.

• It is implemented by using reserved words while, if, and break.

Page 29: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Example: Loop-and-a-Half Control

String name;

while (true) {

name = JOptionPane.showInputDialog(null, "Your name");

if (name.length() > 0)

break;

JOptionPane.showMessageDialog(null, "Invalid Entry.\n" +

"You must enter at least one character.");

}

Page 30: Loop variations do-while and for loops. Do-while loops Slight variation of while loops Instead of testing condition, then performing loop body, the loop

Pitfalls for Loop-and-a-Half Control

• Be aware of two concerns when using the loop-and-a-half control:– The danger of an infinite loop. The boolean

expression of the while statement is true, which will always evaluate to true. If we forget to include an if statement to break out of the loop, it will result in an infinite loop.

– Multiple exit points. It is possible, although complex, to write a correct control loop with multiple exit points (breaks). It is good practice to enforce the one-entry one-exit control flow.


The While Loop - Trinity College, Dublin · 1! 6 While Loops 1 The While Loop! 1E3! Topic 6! 6 While Loops 2 Objectives!! To recognise when a WHILE loop is needed.!! To be able to

Chapter 5: Repetition Statements. In this chapter, you will learn about: Basic loop structures while loops Interactive while loops for loops Loop programming

Loops ISYS 350. Two Types of Loops while loop for loop

1 Chapter 5 Loops. 2 Outline 1. Motivate Loop Statement 2. While Loop Statement 3. do-while Loop Statement 4. for Loop Statement 5. Infinite Loops 6

Loops For While Do While. Loops Used to repeat something Loop statement creates and controls the loop

For Loops › for (variable set; condition; incremental or decrement){ // loop beginning › } // loop end While loops › while (condition) { // beginning

Loops(2) do-while, forceng198.cankaya.edu.tr/uploads/files/ceng198 week6.pdf · Do While Loop do-while loop is the same as while loop except that the condition is checked at the end

Loops (While and For)vlm1.uta.edu/.../lectures/08a_loops.pdf · while loops •A while loop is defined as follows: while (condition) { line 1 line 2 … line n } • condition is

Lecture 3: Loops The While Loop · The While Loop 3 While Loops The while loop. A common repetition structure.! Check a boolean expression.! Execute a sequence of statements.! Repeat

Unit 3. while loops Categories of loops definite loop: Executes a known number of times. The for loops we have seen are definite loops. Print "hello"

Loops ISYS 350. Three Types of Loops while loop do while loop for loop

PROBLEM SOLVING WITH LOOPS - WordPress.com · The loop logic structure There are three types of loop structures: The While/WhileEnd loop Which repeats instructions while a condition

Loops - York University · Converting between for and while Loops (1) To convert a while loop to a for loop, leave the initialization and update parts of the for loop empty. while(B)

Chapter 7 Loops - FTMS...PROG0101 Fundamentals of Programming 23 Loops DO-WHILE Loop • Like a while loop, a do-while loop is a loop that repeats while some condition is satisfied

Loops For loop for n = [2 5 8 7 3] code end While loop while a ~= 3 code end

ROBOTC for CORTEX While Loops Part 1. While Loops A while loop is a structure within ROBOTC which allows a section of code to be repeated as long as a

Intro to Loops 1.General Knowledge 2.Two Types of Loops 3.The WHILE loop 1

For loop Khairul anwar. Loops are used when you need to repeat a set of instructions multiple times. Two type of loops; for loops and while loops How

MATLAB Loops and Branching. Loop types Counted loops; called for loop Conditional loops; called while loop

1 Loops. 2 Topics The while Loop Program Versatility Sentinel Values and Priming Reads Checking User Input Using a while Loop Counter-Controlled (Definite)

Chapter 8 Loops while loop syntax

Topic 14 while loops and loop patterns - University of Texas at …chand/cs312/topic14_while... · 2020-01-09 · Categories of loops definite loop: Executes a known number of times

While and If-Else Loops ROBOTC Software. While Loops While loop is a structure within ROBOTC Allows a section of code to be repeated as long as a certain

JavaScript 101 - UMKC WordPress · Loops • Useful if you want to repeat code execution • for loops • while loops • do…while loops. for loop for(i = 0; i < 10; i ++) {document.write

30/10/20151 3.4 Iteration Loops Do While (condition is true) … Loop

1.6 Loops academy.zariba.com 1. Lecture Content 1.While loops 2.Do-While loops 3.For loops 4.Foreach loops 5.Loop operators – break, continue 6.Nested

Loops in Python - GitHub PagesRepetition with a while loop • while condition: # executes over and over until a condition is False • While loops won’t run at all if condition

CS201 - Repetition loops. Types Of Loops Counting Loop (while, for) Sentinel-Controlled Loop (while, for) Endfile-Controlled Loop (while, for) Input Validation

while Loops · Recall: For Loops for xin grades : print(x) • loop sequence: grades • loop variable: x • body: print(x) To execute the for-loop: 1. Check if there is a “next”

Conditional loops while do while Counting loops for loops Arrays Recursion

Topic 15 Indefinite Loops - While Loops 15 Indefinite Loops - While Loops ... While loop flow chart 8The execution of a while loop can be depicted as ... – Print out the sum and

Lesson 12 While and do while Loops 4th.GWB - 1/10 - Fri ...mrcromano.weebly.com/uploads/3/7/4/4/37445829/... · The do-while loop. A do-while loop is exactly the same as a while-loop

Chapter 5 Loops Section 1 - While Loops Section 2 - For Loops Section 3 - printf Statements Section 4 - Loop Errors Section 5 - Nested Control Statements

The While Loop - Trinity College, Dublin While Loops 1 The While Loop! 1E3! Topic 6! ... 6 While Loops 7 Flowchart for while! ... read 20 numbers, and average them!!

More loops Horstmann Ch 7 continued.. The do-loop continue- condition ? loop-body statements next statement false true WHILE-LOOP continue- condition?