1. Introduction to programming in java
Lecture 07
Conditional if statements

2. Basic boolean Operators
Meaning
Example ==
equal
(4-2)==(8-6) is true !=
Not equal
3 !=2 is true but 4!=(6-2) is false
>
Greater than
(3>2) is true
>=
Greater or equal
(3>=2) is true
<
Less than
(3<2) is false
<=
Less or equal
(3<=4) is true

3. Compound Boolean expressions
Operator
Meaning
Example
&&
And
True && true is true
(3>2) && (1<=10) is true
True && False is False
(3>2) && (1>10) is False
False && False is false
(3<2) && (1>10) is False || OR
True || true is true
(3>2) || (1<=10) is true
True|| False is True
(3>2) || (1>10) is True
False || False is false
(3<2) || (1>10) is False

4. Compound Boolean Expressions (Cont)
True && True = True
False && False = False
(True && False) = (False && True) = False
True || True = True
False || False = False
(True || False) = (False || True) = True
&& ||

5. If – The Conditional Statement
The if statement evaluates an expression and if that evaluation is true then the specified action is taken
if ( x < 10 ) x = 10;
If the value of x is less than 10, make x equal to 10
It could have been written:
if ( x < 10 )
x = 10;
Or, alternatively:
if ( x < 10 ) { x = 10; }

6. Executes a block of statements only if a test is true
The if statement
Executes a block of statements only if a test is true
if (test) {
statement;
... }
Example:
int x = 2;
if (x >= 0) {
System.out.println(“ x is positive");

7. Executes one block if a test is true, another if false
The if/else statement
Executes one block if a test is true, another if false
if (test) {
statement(s);
} else { }
Example:
int x = 2;
if (x >= 0) {
System.out.println(“ x is positive");
else {
System.out.println(“x is negative.");

8. Example1 What does this program do?//
public class IsEven {
public static void main(String[] arguments)
int x = Integer.parseInt(args[0])
if (x % 2 == 0)
System.out.println(“YES”); }
else
System.out.println(“No”);
//end of program

9. Example2 What does this program do?//
public class IsOdd {
public static void main(String[] arguments)
int x = Integer.parseInt(args[0]);
if (x % 2 == 1)
System.out.println(“YES”); }
else
System.out.println(“No”);
//end of program

10. Example3 What does this program do?//
public class FirstIsMultipleOfSecond {
public static void main(String[] arguments)
int x = Integer.parseInt(args[0]);
int y = Integer.parseInt(args[1]);
if (x % y == 0)
System.out.println(“YES”); }
else
System.out.println(“No”);
//end of program

11. Example4 What does this program do?//
public class OneIsMultipleOfOther {
public static void main(String[] arguments)
int x = Integer.parseInt(args[0]);
int y = Integer.parseInt(args[1]);
if ((x % y ==0 ) || (y%x ==0 ))
System.out.println(“YES”); }
else
System.out.println(“No”);
//end of program

12. Example 5 Nested Ifs
// program that takes the exam final mark prints out the corresponding grade.
public class Examgrade {
public static void main(String[] arguments)
double testscore = double.parseDouble(args[0]);
char grade;
if (testscore >= 90)
{ grade = 'A'; }
else if (testscore >= 80)
{ grade = 'B'; }
else if (testscore >= 70)
{ grade = 'C'; }
else if (testscore >= 60)
{ grade = 'D'; }
else
{ grade = 'F'; }
System.out.println("Grade = " + grade); }
//end of program

13. Practice Question
Write a program, DayofTheWeek.java, that takes one command line integer n = 1, 2, ...,7. The program prints the following
n = 1 it prints Monday
n = 2 it prints Tuesday
n = 3 it prints Wednesday
n = 4 it prints Thursday
n = 5 it prints Friday
n = 6 it prints Saturday
n = 7 it prints Sunday
Hints: you can either use
Nested ifs or a switch statement.

14. Solution ( nested if else) DayofTheWeek.java
public class DayofTheWeek {
public static void main(String[] args)
int day = Integer.parseInt(args[0]);
String today;
if(day ==1)
{ today= "Monday";}
else if(day==2)
{today= "Tuesday";}
else if(day == 3)
{today= "Wednesday";}
else if(day==4)
{today= "Thursday";}
else if(day==5)
{today= "Friday";}
else if(day==6)
{today= "Saturday";}
else if(day==7)
{today= "Sunday";}
else
{today= "Wrong number Entered";}
System.out.println(" Today is " + today); }
//end of program