Control Structures: while, for, do...while, break, continue (Java)

1. CiS 260: App Dev I Chapter 4: Control Structures II

2. The while Loop (Repetition) • You often need to repeat the same statements in a program many times. • Repetition or __________ structures allow this. • The Java while statement has this syntax while( expression ) statement ; • The expression, called a loop _________, is the decision-maker and is either true or false. • The statement is called the ______ of the loop. • The statement executes continuously while the expression is ______. • Watch out for _________ loops.

3. Example T expression statement F i = 0 while( i <= 20 ) { System.out.print( i + “ ” ); i = i + 5; } • The output is ____________ • The variable i is called the loop ___________ variable. • When i reaches the value of ____, flow leaves the loop.

4. Counter-Controlled while Loops • If you know in advance how many times a loop is to execute, you can use a ________ variable. final int N = 4; int counter = 0; while( counter < N ) { System.out.print( “Hello ” ); counter++; } • The output is ___________________________

5. Sentinel-Controlled while Loops • If you don’t know in advance how many times a loop is to execute, you can use a ________. final int SENTINEL = -999; int number; while( number != SENTINEL ) { number = Integer.parseInt(keyboard.readLine()); System.out.println( number + “ ” ); } • The output is the series of numbers typed by the user until the user types _______.

6. Other while Loops • Flag-controlled while loops • A _________ variable controls the loop boolean found = false; while( ! Found ) { System.out.println( “Did you find it?” ); answer = System.in.read(); if( answer == ‘y’ || answer == ‘Y’ ) found = true; } • EOF-Controlled while loops • If reading data from a file, a loop can test each line of data read. • When the line doesn’t exist (EOF), the loop stops.

7. The for Loop (Repetition) • The while loop is used for any kind of repetition. • The for loop is equivalent to a counter-controlled __________ loop. • The syntax is for ( initial statement; loop condition; increment statement ) statement; • The initial statement is executed only once. • The loop condition is then evaluated. If _____, the loop statement (block) is executed and the increment statement is executed. • Then the previous step is repeated.

8. Examples of for Loops for( i = 1; i <= 5; i++ ) { System.out.print( “Hello” ); System.out.println( “ everyone” ); } • The output “Hello everyone” appears __ times. • Without the braces, “ everyone” appears _____. int N = 5, sum = 0; for( counter = 1; counter <= N; counter++ ) sum = sum + counter; System.out.println( sum ); • The output of the previous statements is _____.

9. The do…while Loop (Repetition) • The syntax of the do…while statement is do statement while ( expression ) ; • The expression is called the _____ condition. • The statement is always executed at least once. • Then the expression is evaluated. If true, the statement is executed again, and so on.

10. Example of do…while i = 0; do { System.out.print(i + “ ”); i = i + 5; } while( i <= 20); • The output from the above is ______________.

11. break and continue • break is used to • Skip the remainder of the switch structure • Exit early from a loop • continue causes the remaining statements in the loop to be skipped and continues with the next iteration.

12. Nested Control Structures • Nesting is placing control structures (such as if…else) within control structures (such as while). • One author states, “…nesting of control structures provides new power, subtlety, and complexity.”