conditionals & boolean operators

Conditionals & boolean operators

Chapter 3

Condition Statement

• A conditional statement is sometimes called a selection statement.

• Each decision is based on a boolean expression called a condition.

Relational Operators

Relational Operators:

Operation equal to

not equal to

greater than

less than

less than or equal to

greater than or equal to

Algebra =

≠

>

<

≤

≥

Java ==

!=

>

<

<=

>=

Note 1: You can not have a space between !=, ==, > =, or < = Note 2: You can not have =!, =>, or =<

boolean expression use relational operators to make a decision

Logical Comparison Operators

Condition In Math In ProgrammingA 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 < B

A is greater than B A > 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

Six different comparison operators are used in mathematics and computer programming.

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

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

boolean Logic Operators

&& AND

|| OR

! Not

Sometimes 2 conditions need to be checked.

Compound boolean expression use logic operators in boolean expressions.

answer = (x > 7 && x == 9)

answer = (x > 7 || x == 9)

Both conditions must be true

Only one condition needs to be true

answer = !(x > 7 || x == 9)

Not reverses the result (opposite)

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

Writing boolean statements with && AND

• And operator will be true only if both expressions evaluate to true.

a b a && b

true true true

true false false

false true false

false false false

Writing boolean statements with && AND

int x = 2 int y = 90 (x < 10 && y < 97)

(x > 10 && y < 97)

• (If one were false the whole thing would be false.)

False True

Condition would produce True

Condition would produce False

T T

Writing an or || boolean statement:

a b a || b true true true true false true false true true false false false

The outcome will be true as long as one of the expressions evaluates to true.

Boolean Operators

• int x = 2 int y = 90

• Writing an or || boolean statement:

• (x < 10 || y < 97)

• (x > 10 || y < 97)

True

False

True

True

Condition would produce True

Condition would produce True

Boolean Operators Not !

• It reverses the value of a boolean expression

a outcome

True False

False True

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))

!True

!False

True

True

Condition would produce False

Condition would produce True

True True

!True

Writing Boolean StatementsYou must write the full condition when using logic operators ):

1. x > y > z

2. x and y are both less than 0

3. neither x nor y is less than 0

4. 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));

Operator precedence

Operator Associativity

* / % left to right+ - left to right< <= > >= left to right== != left to right&& (and) left to right|| (or) left to right= += -= *= /= right to left

if, if-else, if-else-if-else StatementsThe if-else class of statements should have the following form

if (condition) {statements;} else {statements;}

if (condition) {statements;} else if (condition) {statements;} else if (condition) {statements;}

if (condition) {statements;}

Conditional StatementsProgramming 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

statement;

if (boolean condition) {

statement;

statement;

}

else {

statement;

statement;

}Curly brackets optional

Curly brackets required

Conditional StatementsNested 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 AYour grade is BYour grade is C

Conditional StatementsNested 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

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.

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 AFirst if statementYour grade is BSecond if statementYour grade is CThird if statementLast if statement

What prints

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

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");

If(total = 25);{}

if(total == 10){}

Do not capitalize if

Use the == to show equality