1. Conditionals & boolean operators
Chapter 3

2. Condition Statement
A conditional statement is sometimes called a selection statement.
Each decision is based on a boolean expression called a condition.

3. Relational Operators
boolean expression use relational operators to make a decision

4. Logical Comparison Operators
Six different comparison operators are used in mathematics and computer programming.
Condition
In Math
In Programming
A equals B
A = B
A = B or A == B
A is not equal to B
A  B
A != B
A is less than B
A < B
A is greater than B
A > B
A is less than or equal to B
A  B
A <= B
A is greater than or equal to B
A  B
A >= B

5. Logical Conditions
Logical comparisons that are either true or false are most often used as the basis for the true and false values in Boolean logic.
They are often used for simple conditions in branching and looping instructions.
if (hours > 40)
pay overtime
if (age < 12)
stay in the back seat
while (count  10)
print count increment count

6. 100th Anniversary Edition
Boolean Logic
Boolean logic is a form of mathematics in which the only values used are true and false.
Boolean logic is the basis of all modern computing.
There are three basic operations in Boolean logic – AND, OR, and NOT.
100th Anniversary Edition

7. boolean Logic Operators
Sometimes 2 conditions need to be checked.
Compound boolean expression use logic operators in boolean expressions.
&& AND
|| OR
! Not
answer = (x > 7 && x == 9)
Both conditions must be true
answer = (x > 7 || x == 9)
Only one condition needs to be true
answer = !(x > 7 || x == 9)
Not reverses the result (opposite)

8. Compound Conditions
Compound Boolean conditions can be created using the Boolean AND, OR and NOT operations in branching and looping instructions.
if ( (hours > 40) && (type = hourly) )
pay overtime
if ( (age < 12) || (height < 42 in.) )
stay in the back seat
while ( (count <= 10) && ! (status = away) )
print name.count increment count

9. Writing boolean statements with && AND
And operator will be true only if both expressions evaluate to true. a b
a && b
true
false

10. Writing boolean statements with && AND
int x = int y = 90
(x < 10 && y < 97)
(x > 10 && y < 97)
(If one were false the whole thing would be false.)
Condition would produce True T T
Condition would produce False
False
True

11. Writing an or || boolean statement:
The outcome will be true as long as one of the expressions evaluates to true. a b
a || b
true
false

12. Boolean Operators int x = 2 int y = 90
Writing an or || boolean statement:
(x < 10 || y < 97)
(x > 10 || y < 97)
Condition would produce True
True
True
Condition would produce True
False
True

13. Boolean Operators Not ! It reverses the value of a boolean expression
outcome
True
False

14. Boolean Operators Not ! int x = 2 int y = 90
Writing an && with ! boolean statement:
(!(2 < 10) && (90 < 97))
!((2 < 10) && (90 < 97)) Reverses the whole things after evaluated. Condition would produce false
(!(2 > 10) && (90 < 97))
Condition would produce False
!True
True
True
True
!True
Condition would produce True
!False
True

15. Writing Boolean Statements
You must write the full condition when using logic operators ):
x > y > z
x and y are both less than 0
neither x nor y is less than 0
x is equal to y but not equal to z
(x>y && y > z);
(x<0 && y<0);
!(x<0 && y<0);
(!(x<0) && (!y<0));
((x==y) && (!x==z));

16. Operator precedence Operator Associativity * / % left to right + -
< <= > >=
== !=
&& (and)
|| (or)
= += -= *= /=
right to left

17. if, if-else, if-else-if-else Statements The if-else class of statements should have the following form
if (condition) {
statements; }
else if (condition) {
if (condition) {
statements; }
else {
if (condition) {
statements; }

18. Conditional Statements
Programming style
Note that if there is only a single statement in the if or else block, curly brackets are not needed. If there is more than one statement in one of these blocks, the curly brackets are required.
if (boolean condition)
statement;
else
if (boolean condition) {
statement; }
else {
Curly brackets optional
Curly brackets required

19. Conditional Statements
Nested if statements
If statements will execute every if that is true
public void grade(int testScore) {
if (testScore >= 90)
System.out.println("Your grade is A");
if (testScore >= 80)
System.out.println("Your grade is B");
if (testScore >= 70)
System.out.println("Your grade is C");
else
System.out.println("Your grade is F"); }
testScore = 90
Your grade is A
Your grade is B
Your grade is C

20. Conditional Statements
Nested if statements
When you use the if else structure, it will stop and execute the first if else that is true.
public void grade2(int testScore) {
if (testScore >= 90){
System.out.println("Your grade is A"); }
else if (testScore >= 80 ){
System.out.println("Your grade is B");}
else if (testScore >= 70 ){
System.out.println("Your grade is C"); }
else{
System.out.println("Your grade is F"); } }
testScore = 90
Your grade is A

21. No braces?
if (condition) //AVOID! THIS OMITS THE BRACES {}! statement; If you do not use braces the first statement after the if condition is the only one that goes with it.

22. Need braces
public void grade2(int testScore) { if (testScore >= 90) System.out.println("Your grade is A"); System.out.println("First if statement"); if (testScore >= 80) System.out.println("Your grade is B"); System.out.println("Second if statement"); if (testScore >= 70) System.out.println("Your grade is C"); System.out.println("Third if statement"); if(testScore < 70) System.out.println("Your grade is F"); System.out.println("Last if statement"); }
testScore = 90;
Your grade is A
First if statement
Your grade is B
Second if statement
Your grade is C
Third if statement
Last if statement

23. What prints int i=3; if(i<10) System.out.println("hello");
System.out.println("goodbye");

24. What prints
int i=3, j=14; if(i<10) System.out.println("hello"); if(j>10) System.out.println("howdy"); System.out.println("goodbye");

25. common errors If(total = 25); { } if(total == 10) Do not capitalize if
Use the == to show equality