Flow of Control Recitation – 09/(18,19)/2008 CS 180 Department of Computer Science, Purdue University

Now posted on the class webpage. Due Wed, Sept. 24 at 10 pm. Start early. All questions on the class newsgroup. Exam in 2 weeks (10/1); Consult Mentor (Debbie) for more on pattern, advice etc. Evening consulting hours. LWSN B146. MTW 7-10 pm. Project 3 and Exam

Loop statements while do-while for break and continue statements Display text in Applets Outline

A portion of a program that repeats a statement or a group of statements is called a loop The statement or group of statements to be repeated is called body of the loop A loop could be used to compute sum of N numbers What are Loops?

while loop continuously executes a block of statement until a particular condition is true Syntax while (boolean_expression) { statement; } The while statement

Example: int count = 1; while (count < 11) { System.out.println ("Count is: " + count); count++; } while statement example

The do-while statement Similar to a while statement, except that the loop body is executed at least once Syntax do { Statement; } while (Boolean_Expression); Remember the semicolon at the end of while. It helps the compiler to distinguish do-while and while statements

Example: int count = 1; do { System.out.println ("Count is: " + count); count = count+1; } while (count<=10); do-while statement example

Syntax for (Initialization; Condition; Update) { statement; } Initialization expression initializes the loop and is executed once at the beginning Loop terminates when the Condition evaluates to false Update can be an increment or a decrement on a variable. It is executed after the first iteration The for statement

for statement example 1  The action of the for loop in listing 4.5

Example: Print all even numbers in the first 10 numbers for (int count =1; count<=10;count++) { if(count%2 == 0) System.out.print(count+” ”); } Output: for statement example 2

Useful to operate on collection of data such as enumeration Example enum Names {James, Joshua, Scott} for (Names name: Names.values()) System.out.println(name+” ”); Names.values() represent all the values in the enumeration. The for-each statement

The break statement break statement can be used to end the loop immediately Example: for (int n=1; n<=5;n++) { if (n==3) { break; } System.out.print(n+” ”); } Output: 1 2

The continue statement A continue statement ends current loop iteration and begins next iteration Example: for (int i = 0; i < 10; i++) { if (i == 5) { continue; } System.out.print(i+” ”); } Output: It is recommended to sparingly use break and continue statements

loops in Applets A multiface Applet Uses loop to draw several smiley faces Uses if statement to alter appearance View sample program, listing 4.9 class MultipleFacessample program

drawString Method Similar to drawoval method, but displays text Example canvas.drawString("Hello",10, 20); Writes word Hello at point (10, 20) Used to place "Kiss, Kiss" and "Tee Hee" on screen in listing 4.9