1. IMPLEMENTING NESTED LOOP
Chapter 5.3:

2. Nested Loops
 The placing of one loop inside the body of another
loop is called nesting.
 When you "nest" two loops, the outer loop takes
control of the number of complete repetitions of
the inner loop.
 While all types of loops may be nested, the most
commonly nested loops are for loops.

3. Nested for Loops
 When working with nested loops, the outer loop
changes only after the inner loop is completely
finished (or is interrupted.).

4. Example 8
Output ?
0 0
0 1
1 0
1 1
2 0
2 1
int num1, num2;
for(num2 = 0; num2 <= 2; num2++)
{
for(num1 = 0; num1 <= 1; num1++)
{
System.out.println(num2 + " " + num1);
}
}

5. Infinite Loop
 By using any repetition statements, make sure that
the loop will eventually terminate.
 An infinite loop occurs when a condition always
evaluates to true and continues to execute
endlessly.
int product =0;
for (product = 0;product < 10;)
{ product = product * 2;
System.out.println(product);
}

6. Repetition Control Structures
Repetition can be controlled by:
 Counter controlled loop
 Sentinel controlled loop
 Flag controlled loop

7. Counter Controlled Loop
 Know exactly how many times a set of statements
needs to be executed.
Output ? 1 3 5 7 9
int num =1;
while (num < 10)
{
System.out.print (num);
num = num +2;
}
Example 10:

8. Sentinel Controlled Loop
 You might not know exactly how many times a set
of statements needs to be executed.
 It uses a "special" or sentinel value to indicate that
the loop is to end.
 This must be a value that doesn't occur normally in
the data.

9. Example 11 (complete program)
import java.util.Scanner;
class sentinelLoop {
public static void main (String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter an Integer, or -1 to stop: ");
int choice= input.nextInt();
while (choice!=-1)
{
System.out.println("INSIDE LOOPING");
System.out.print("Enter an Integer, or -1 to stop: ");
choice= input.nextInt();
}
System.out.println("Sentinel value detected. Good Bye.");
}
}

10. Example 11 ….
Enter an Integer, or -1 to stop: 2
INSIDE LOOPING
Enter an Integer, or -1 to stop: 5
INSIDE LOOPING
Enter an Integer, or -1 to stop: 0
INSIDE LOOPING
Enter an Integer, or -1 to stop: -1
Sentinel value detected. Good Bye.
OUTPUT?

11. Flag Controlled Loop
 Use a boolean variable to control the loop
boolean found = false;
while (!found){
:
:
if(expression)
found = true;
}

12. Exercise 1:
 What is the output of the following program?
public class LoopExercise1
{
public static void main (String args[])
{
int choice=1, total=0;
while (choice <4){
total = choice++;
System.out.print(total); }
}
}

13. Exercise 2:
 What is the output of the following program?
public class LoopExercise2
{
public static void main (String args[]){
for (int number =2; number <20; number++)
{
number = number *2;
if (number <15)
System.out.println(number);}
}
}

14. Exercise 3:
 How many times is the following loop body
repeated?
public class LoopExercise3 {
public static void main (String args[])
{
int i=1;
do {
if ((i % 2)== 0)
System.out.print(i);
i++;
} while(i<5);
}
}