Three kinds of looping structures

1
Three kinds of looping structures

• The while loop
• The for loop
• The do (also called the do-while) loop
• All have equivalent power, e.g., if you can write
  the program using a do loop you could also write
  the program using a for loop

2
A simple while loop example

• public class Sum
• public static void main( String args)
• final int MIN 1, MAX 100
• int count MIN, sum 0
• while (count lt MAX)
• sum count
• count
• System.out.println("the sum of the
  number between "
• MIN " and " MAX " is "
  sum)

3
Equivalent for loop

• public class Sum
• public static void main( String args)
• final int MAX 100, MIN 1
• int sum 0
• for (int count MIN count lt MAX count)
• sum count
• System.out.println("the sum of the
  number between "
• MIN " and " MAX " is "
  sum)

4
A do loop example

• import cs1.Keyboard
• public class Sum
• public static void main( String args)
• int min, max, sum 0
• do
• System.out.print(enter limits for the sum")
• System.out.println(" both must gt 0")
• minKeyboard.readInt()
• maxKeyboard.readInt()
• while (min lt 0 max lt 0)
• for (int count min count lt max count)
• sum count

5
Choosing a looping structure --- rule of thumb
guidelines

• Use a do loop or a while loop when the number of
  iterations can not be known in advance
• Use a for loop for counting
• Use a do loop when the body of the loop must be
  executed before evaluating the loop test

6
A silly game version 1

• import cs1.Keyboard
• public class Guess
• public static void main( String args)
• final int MYNUMBER 3
• System.out.print("guess a number between 1
  10 ")
• int guess Keyboard.readInt()
• if (guess MYNUMBER)
• System.out.println("You got it!!!")
• else
• System.out.println("Sorry, that's wrong")

7
A silly game version 2

• import cs1.Keyboard
• public class Guess
• public static void main( String args)
• final int MYNUMBER 3
• int guess
• do
• System.out.print("guess between 1 10 ")
• guess Keyboard.readInt()
• if (guess MYNUMBER)
• System.out.println("You got it!!!")
• else
• System.out.println("Sorry, that's wong")
• while (guess ! MYNUMBER)

8
A silly game version 3

• Add a loop to repeat the game in class