ifelse

1
if-else

• if (condition)
• statements1
• else
• statements2
• if within else
• if (condition1) statements1
• else
• if (condition2) statements2
• statements3

2
if-else if-else if--else

• if (condition1)
• statements1
• else if (condition2)
• statements2
• else if (condition3)
• statements3
• else
• statementsn

3
Example

• class greetings
• public static void main(String arg)
• int hour 3
• if ((hour gt 0) (hour lt 12))
• System.out.println(Good Morning!)
• else if ((hour gt 12) (hour lt 18))
• System.out.println(Good
  Afternoon!)
• else if ((hour gt18) (hour lt 24))
• System.out.println(Good
  Evening!)
• else
• System.out.println(Bad time!)

4
Dangling else

• / Write comments here
• /
• class dangle
• public static void main (String args)
• int shape,circle,rectangle,radius,distance
• circle1
• rectangle2
• radius5
• distance6
• shape1
• if (shapecircle)
• if (radius gt distance)
• System.out.println("Point is enclosed in the
  circle")
• else System.out.println("Point is not
  enclosed in the circle")

5
Loops

• Needed in problems that require solving the same
  subproblem over and over
• Computing the sum of the first 100 natural
  numbers and putting the result in y
• Algorithm
• y 1
• y y 2
• y y 3
• y y 100
• Cannot write 99 such additions use a loop

6
while

• while (condition)
• statements
• Can put anything in statements
• The entire construct is called a while loop
• statements are executed until condition is true
• Even before executing it the first time condition
  is evaluated
• A while loop may not execute even once

7
Example

• class justAnExample
• public static void main(String arg)
• int x 5
• int y 0
• while (x lt 10)
• y--
• x
• System.out.println(y)

8
Example

• class justAnExample
• public static void main(String arg)
• int x 15
• int y 0
• while (x lt 10)
• y--
• x
• System.out.println(y)

9
Sum of natural numbers

• class naturalSum
• public static void main(String arg)
• int n 2
• int y 1
• while (n lt 100)
• y n
• n
• System.out.println(Sum of the first
  (n-1) natural numbers is y)