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 boolean expression use relational operators to make a decision

Logical Comparison Operators 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 Sometimes 2 conditions need to be checked. Compound boolean expression use logic operators in boolean expressions. && AND || OR ! Not Both conditions must be true Only one condition needs to be true 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.

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.) Condition would produce True T T Condition would produce False False True

Writing an or || boolean statement: 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) Condition would produce True True True Condition would produce True False True

Boolean Operators Not ! • It reverses the value of a boolean expression

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

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));

Operator precedence

if, if-else, if-else-if-else StatementsThe if-else class of statements should have the following form if (condition) { statements; } else if (condition) { statements; } else if (condition) { statements; } if (condition) { statements; } else { statements; } if (condition) { statements; }

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 statement; if (boolean condition) { statement; statement; } else { statement; statement; } Curly brackets optional Curly brackets required

Conditional Statements Nested if statements If statements will execute every if that is true public void grade(inttestScore) { 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

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(inttestScore) { 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(inttestScore) { 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

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

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

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

Conditionals & boolean operators