Download
1 / 11
110 likes | 210 Views
This guide covers essential programming control structures such as while loops, do-while loops, and for loops, including practical examples and their syntax. It introduces the Acrobat class, which performs specific actions like clapping, knee bends, and reporting completed exercises—demonstrating object-oriented programming principles. The document also addresses common pitfalls, such as infinite loops caused by logic errors or incorrect syntax, and the importance of terminating conditions in loops. Suitable for beginners and intermediate programmers seeking to solidify their understanding of looping constructs.
E N D
Agenda Classes vs Objects Role play Loop structures while loop do-while loop for loop
Class Acrobat An acrobat can do 3 things: 1) Clap his or hands a given number of times. 2) Perform knee bends a given number of times. 3) Report how many exercises have been completed.
Illegal instructions • Acrobat, clap 4 => only Acrobat objects can clap • Andrew, clap => clapping requires a number • Clap 3 => no object specified
while Loop • while loop executes a set of statements over and over again based on a condition. • takes the form: while (<condition>) { <statements> } • Example : Intnum=0; while (num < 5) { num += 1; } • Each execution of the loop is called an iteration.
do-while Loop • Similar to while loop, but the condition is not evaluated until after the first execution of the loop. Therefore, the do-while executes at least once. The form: do { <statements> } while (<condition>); • Example: do { System.out.print("Enter a number less than 4:"); playerNum = input.nextInt(); } while (playerNum >= 4);
for Loop • for Loop executes a set of statements a fixed number of times. The for statement takes the form: for (<initialization>; <condition>; <increment>) { <statements> } • example for (int i = 1; i <= 10; i++) { System.out.println(i); } How can this example change to equivalent while or do-while loop?
Infinite Loop • The condition of a loop is used to determine when the loop should stop executing. What happens, though, if the condition never becomes false? intnum = -1; while (num < 0) { num = -1; }
Infinite loop • One example is syntax error- semicolon after the condition; another example of a syntax error that can lead to an infinite loop is omitting the curly braces. while (num < 0); { //do nothing num += 1; } while (num < 0) System.out.println(“Enter a value”); num = input.nextInt();
Infinite loop • A logic error can also lead to an infinite loop condition. intnum = 1; do { num+= 1; } while (num >= 0); • In this case, the loop isn’t infinite because num is eventually assigned a number so large that an overflow results. An overflow occurs when there are not enough bits to store a number.
practice • an application that calculates the average of a set of numbers must sum the numbers and then divide the total by the count. • A run of the application looks simliar to: Enter a value( 0 to quit): 25 Enter a value( 0 to quit): 14 Enter a value( 0 to quit): 9 Enter a value( 0 to quit): 120 Average: 42.0
pseudocode Prompt user for a value while (value != 0) count value add value to sum of values prompt user for another value Display average of values (sum/count)
