CSCI 144 - Introduction to Computer Science Instructor: John - - PowerPoint PPT Presentation

CSCI 144 - Introduction to Computer Science

Instructor: John Goettsche Computer Science Department Pacific Lutheran University Spring 2018

1

More Boolean Expressions and If Statements

Flags

Flags

if (distanceToHole < 30)

• nGreen = true;

boolean onGreen = false; if (onGreen) System.out.println("Get out your putter!");

Boolean variable Monitor some condition Can be set And later tested

Comparing Characters

Comparing Characters

< > <= >= == != Characters can be compared

using relational operators

0000000001000011 char ch = ‘C’;

Unicode is stored as a 16 bit number

Comparing Characters

char c = ′A′; if(c < ′Z′) System.out.println("A is less than Z"); < > <= >= == != Characters can be compared

using relational operators

0000000001000011 char ch = ‘C’;

Unicode is stored as a 16 bit number ‘0’ … ‘9’ ‘?’ ‘A’ … ‘Z’ ‘a’ … ‘z’ Characters are ordinal -- they have an order

Character Unicode 'A' 65 'B' 66 'C' 67 'D' 68 ... ... 'Z' 90 Character Unicode 'a' 97 'b' 98 'c' 99 'd' 100 ... ... 'z' 122

Comparing Strings

“Sally”

name1 String name1, name2;

“Sally”

name2 if (name1 == name2) System.out.println(“The names are equal”);

Can’t compare strings with ==

“Sally”

name1 String name1, name2;

“Sally”

name2 if (name1.equals(name2)) System.out.println(“The names are equal”);

Must use equals method

“Sally”

name1 String name1, name2;

“SALLY”

name2 if (name1.equalsIgnoreCase(name2)) System.out.println(“The names are equal”);

Logical Operators

Logical Operators

Operator Meaning Effect

&& AND Both expressions must be true for the overall expression to be true. || OR One or both expressions must be true for the overall expression to be true. ! NOT The ! operator reverses the truth of a boolean expression.

AND &&

Expression 1 Expression 2 Expression1 && Expression2 true false false true false false true true

OR ||

Expression 1 Expression 2 Expression1 || Expression2 true false false true false false true true

NOT !

Expression 1 !Expression1 true false

Precedence

Order of Precedence Operators Description

1 (unary negation) ! Unary negation, logical NOT 2 * / % Multiplication, Division, Modulus 3 + - Addition, Subtraction 4 < > <= >= Less-than, Greater-than, Less-than or equal to, Greater-than or equal to 5 == != Is equal to, Is not equal to 6 && Logical AND 7 || Logical OR

Practice

Logical Operators

Evaluate the following expressions given these values for Boolean variables x, y, and z:

boolean x = true, y = false, z = true; Expression Result x && y || x && z __________ (x || !y) && (!x || z) __________ x || y && z __________ !(x || y) && z __________

Boolean Expressions

Evaluate the following expressions given these variables:

int count = 0, limit = 10, x = 5, y = 7; char midtermGrade = ‘A’; Expression Result count == 0 && limit < 20 __________ limit > 20 || count < 5 __________ !(midtermGrade != ‘C’) __________ (count < 10) || (x < y) __________

Boolean Expressions (cont.)

Evaluate the following expressions given these variables:

int count = 0, limit = 10, x = 5, y = 7; char midtermGrade = ‘A’; Expression Result !(((count < 10) || (x < y)) && (count >= 0)) __________ ((limit/count) > 7) || (limit < 20) __________ ((midtermGrade == ‘A’) || ((limit/count) < 20) __________ (limit < 0) && ((limit/count) > 7) __________

Write an if statement to calculate tax (totalSales times TAXRATE) if the user input forProfit is ‘Y’ or ‘y’.

if (forProfit == ‘Y’ || forProfit == ‘y’) { tax = totalsales * TAXRATE; }

Write an if statement to calculate tax (totalSales times TAXRATE) if the user input response is “yes” (be sure to ignore case).

if (response.equalsIgnoreCase(“yes”)) { tax = totalsales * TAXRATE; }

Write an JAVA program, scan user’s input as temperature and mood, write if statement to print “Play golf!” if the temperature is between 65 and 80, and mood is “happy”. For all other cases, print ‘Programming at home’. (hint: consider ‘flags’)

Reference: Tables and flowcharts adapted from Starting Out with Java by T. Gaddis Chapter 3 Slides.