Chapter 9

Control Structures

Learning Java through Alice © Daly and Wrigley

Objectives•Code programs using the following looping techniques: ▫While Loop ▫Do While Loop ▫For Loop

• Explain when the Break and Continue statements would be used when coding loops.

•Walk through While, Do While, and For loops documenting variables as they change.

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while loop

While Syntax: Flowchart:

while (boolean condition) {         repeated statements   }

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while loop example:

While : Output:

int counter = 1;  while (counter <=5)  {        System.out.println ("Hello " + counter);        counter ++; }

Hello 1 Hello 2 Hello 3 Hello 4 Hello 5

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do while loopDo While Syntax: Flowchart:

do {          repeated statements   } while (boolean condition);

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do while loop example:Do While : Output:

Hello 1 Hello 2 Hello 3 Hello 4 Hello 5

int counter = 1;  do { System.out.println("Hello " + counter);  counter++; }  while (counter <=5);

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for loopfor (initialization;   test;    increment)  {            statements; }

Initialization - initializes the start of the loop.

Example: int i = 0;Boolean Test - occurs before each pass of the loop.

Example: i<10;Increment - any expression which is updated at the end of each trip through the loop.

Example: i ++,   j+=3 Statements are executed each time the loop is executed.

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for loop logic

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for loop example 1:for loop Results

for (int counter =1;  counter <=5;  counter++ ) { System.out.println ("Hello  " + counter);}

Hello 1 Hello 2 Hello 3 Hello 4 Hello 5

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for loop example 2:for loop with modulus results

for (int number = 0;   number <1000;   number++) {           if ( number  %  12  = =  0 )  {                    System.out.println("Number is " + number);  }}

..... etc. Number is 996

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for loop example 3:for loop to print even numbers from 1 to 20 results

  

for (int number = 2;   number <=20;   number+=2) {          System.out.println("Number is " + number); }

The number is 2The number is 4The number is 6The number is 8The number is 10The number is 12The number is 14The number is 16The number is 18The number is 20

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for loop example 4:for loop with multiple initialization & increments results

  for (int i=0,  j=0 ;  i*j < 1000;  i++,  j+=2) {       System.out.println( "The answer is " + i + " * " + j + " = " + i*j );  }

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Break Statement

for (int   index =1;   index<= 1000;    index ++)  { if (index   ==   400) { break; }  System.out.println("The index is " + index); }

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Continue Statement

for (int index = 1, index <= 1000; index ++) {  if (index == 400)  { continue;  } System.out.println("The index is " + index); }

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