1. if-else if (condition) { statements1 } else { statements2
if within else
if (condition1) { statements1 }
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 >= 0) && (hour < 12)) {
System.out.println(“Good Morning!”); }
else if ((hour >= 12) && (hour < 18)) {
System.out.println(“Good Afternoon!”);
else if ((hour >=18) && (hour < 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;
circle=1;
rectangle=2;
radius=5;
distance=6;
shape=1;
if (shape==circle) {
if (radius >= distance)
System.out.println("Point is enclosed in the circle");
else System.out.println("Point is not enclosed in the circle"); }
else System.out.println("Shape is not 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 < 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 < 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 <= 100) {
y += n;
n++; }
System.out.println(“Sum of the first ” + (n-1) + “ natural numbers is ” + y);