Lesson Goals Learn the following three repetition methods, their
similarities and differences, and how to avoid common errors when using them: while do-while for
Learn nested looping Learn how to use break statements to exit a loop Begin to learn how to deal with situations where
faulty or out of range input is supplied
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Introduc$on to Loops Many of the tasks performed by computers require repetition, often massive
repetition
Using repetitive syntax can make your code more concise and easier to write
and debug
Java has three types of repetitive constructs (also known as loops): while, do-
while or for Loops are built out of several fundamental statements because there are three things (in each of the three types of loops) that must be done correctly: The loop must be initialized correctly. The ending condition must be tested correctly. The body of the loop or the loop statement must change the condition that is
tested.
Overlooking one of these aspects results in a defective loop and a sometimes
difficult to find program bug! Usually each of these three considerations is located in a different spot. No wonder that loops often go wrong! You have to plan out the logic of your program in order to effectively use loops and conditionals
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Types of Loops
type
description
counting loop
Uses a loop control variable to count upwards or downwards (usually by an integer increment.)
sentinel-controlled loop
Loop keeps going until a special value is encountered in the data.
result-controlled loop
Loop keeps going until a test determines that the desired result has been achieved.
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The while Statement Here is a program with a loop. It contains a while statement, followed by a block of code. Remember, a block is a group of statements enclosed in braces. // Example of a while loop public class LoopExample { public static void main (String[] args ) { // start count out at one int count = 1; while ( count = 0 ) // count is tested { System.out.println( "count is:" + count ); count = count - 1; // count is changed by -1 } System.out.println( "Done counting down." ); } } 8
The do-while Statement Here is a program with a loop. It contains a do statement, followed by a block of code, followed by a while statement. // Example of a do-while loop that executes only once public class DoWhileExample { public static void main (String[] args ) { int count = 1000; // initialize do { System.out.println( count ); count++ ; } while ( count < 10 ); // test System.out.println( "Done with the loop" ); } } 9
The Basic Syntax of the do-while Statement do { statement1; statement2; o 0 0 statementn; } while (condition);
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Basic Terminology of the do-while Statement The condition is a Boolean expression: something that
evaluates to true or false. The condition can be complicated, using many relational operators and logical operators. A single statement is allowed Without braces to create a block only one statement is
executed inside the loop
The block or single executable statement is sometimes
called the loop body. The do-while is always executed at least once, if the do statement is executed There is a semi-colon after the while statement in a dowhile
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The for Statement Here is a program with a loop. It contains a for statement, followed by a block of code. A block is a group of statements enclosed in braces. // Example of a for loop public class ForExample { public static void main (String[] args ) { int sum=0; for ( int count = 0; count