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Mastering While Loops: Count and Event Control Techniques in Java

This guide covers the essential concepts of while loops in Java, focusing on both count-controlled and event-controlled loops. You'll learn how to implement pre-test loops to repeat actions while a Boolean condition remains true, and post-test loops using the do-while construct. The tutorial provides hands-on examples such as counting numbers, summing inputs until a sentinel value is encountered, and calculating averages. Enhance your programming skills by understanding how to effectively use loop control variables and manage user input in your applications.

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Mastering While Loops: Count and Event Control Techniques in Java

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  1. 6-1 While Loops (Pre –Test) • while ( boolean condition is true) //enter loop • Count Controlled: count = 0; // Initialize Loop Control Variable (LCV) – Prime loop! while( count < = 10 ) // Enter the loop if LCV check is true { System.out.println(count); count++; // Update LCV – Be careful where you put this! } • Event Controlled : Consider the following & assume a getNum( ) method exists for input: String input; double sum = 0; int num, count =0; num = getNum( ); // Priming read! while ( num != -999 ) // -999 is called a sentinel value (6.4 p247) { count++; sum + = num; num = getNum( ); } System.out.print(“A sum of “ +sum +”,with a count of “ +count +” results in…”);

  2. do – while loop (Post –Test) import javax.swing.JOptionPane; class void Average( ) { //================================================================== public static intgetNum( ) { String input; do //do-while a post-test loop. Why? { input = JOptionPane.showInput Dialog(“Enter number <-999 terminates>”); }while( input = = null || input = =“”); return Integer.parseInt(input); } //================================================================== public static void main( ) { double sum = 0; int num, ave, count =0; num = getNum( ); while ( num != -999 ) { count++; sum + = num; num = getNum( ); } ave = (int)Math.round( sum/ ct ); System.out.print(“ Average of “ +count +” values with a sum of ” +sum +” is “+ave); } }

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