while

1
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

2
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)

3
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)

4
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)

5
Sum of natural numbers

• class naturalSumAnotherWay
• public static void main(String arg)
• int n 99
• int m n1
• int y 100
• while (n gt 0)
• y n
• n--
• System.out.println(Sum of the first
  m natural numbers is y)

6
do-while

• do
• statements
• while (condition)
• statements execute at least once irrespective
  of condition

7
for loops

• for (expression1 condition expression2)
• statements
• Same as
• expression1
• while (condition)
• statements
• expression2

8
Sum of natural numbers

• class naturalSum
• public static void main(String arg)
• int n
• int y 1
• for (n2 n lt100 n)
• y n
• System.out.println(Sum of the first
  (n-1) natural numbers is y)

9
Comma operator in for loop

• for (expression1a, expression2a, condition
  expression1b, expression2b,)
• statements
• Same as
• expression1a
• expression2a
• while (condition)
• statements
• expression1b
• expression2b

10
Sum of natural numbers

• class naturalSum
• public static void main(String arg)
• int n
• int y
• for (n2, y1 n lt100 y n, n)
• System.out.println(Sum of the first
  (n-1) natural numbers is y)

11
Empty for loop body

• for (expression1 condition expression2)
• Same as
• for (expression1 condition expression2)

12
Infinite loops

• Loops that never terminate
• while (true)
• statements
• do
• statements
• while (true)

13
Infinite loops

• for (expression1 expression2)
• statements
• for (i0 i gt -10 i)
• statements
• for (i0 ilt100 i--)
• statements