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

1 CSCI 144 - Introduction to Computer Science Instructor: John Goettsche Computer Science Department Pacific Lutheran University Fall 2017 PLU Computer Science

Before class • Quiz on Monday • Turn-in Buggy codes • Solutions to Buggy codes • CAT QA PLU Computer Science

Boolean Expressions and If Statements PLU Computer Science

Sequential Execution Execution System.out.print("How many credit hours have you taken? "); flow creditHours = scan.nextInt(); System.out.print("How many grade points have you earned? "); gradePoints = scan.nextDouble(); gpa = gradePoints / creditHours; hoursLeft = HOURS_NEEDED - creditHours; System.out.printf("Your GPA is %.2f\n", gpa); System.out.printf("You need %d more hours", hoursLeft); System.out.println(" to complete your degree."); PLU Computer Science 4

Java code Conditional Execution true Is it cold if( coldOutside ) outside? wearCoat(); Wear a coat. false PLU Computer Science 5

if( coldOutside ) { true Is it cold wearCoat(); outside? wearHat(); wearGloves(); Wear a coat. } false Wear a hat. Wear gloves. Curly braces define a block of statements. PLU Computer Science 6

A boolean expression is something that evaluates to a boolean value (true or false) true Boolean Expression? Statement or if( boolean expression ) block false statement or block PLU Computer Science 7

Think/Pair/Share Write down at least two instances where you might have used a conditional in one of your previous lab assignments or pair exercises. PLU Computer Science

Relational Operators PLU Computer Science

Boolean Operators Operator Meaning > is greater than < is less than >= is greater than or equal to <= is less than or equal to == is equal to != is not equal to PLU Computer Science 10

Boolean Expressions Expression Meaning x > y Is x greater than y? x < y Is x less than y? x >= y Is x greater than or equal to y? x <= y Is x less than or equal to y? x == y Is x equal to y? x != y Is x not equal to y? PLU Computer Science 11

GPA Example with Conditional Execution System.out.print("How many credit hours have you taken? "); creditHours = scan.nextInt(); System.out.print("How many grade points have you earned? "); gradePoints = scan.nextDouble(); gpa = gradePoints / creditHours; Note the use of indentation hoursLeft = HOURS_NEEDED - creditHours; and curly braces. System.out.printf("Your GPA is %.2f\n", gpa); if( gpa >= 3.7 ) System.out.println("Wow, you're a hard worker!"); System.out.printf("You need %d more hours to complete your degree.\n", hoursLeft); if( hoursLeft < 0 ) { System.out.println("You can graduate!"); System.out.println("See your advisor to get graduation clearance!"); } PLU Computer Science 12

System.out.print("How many credit hours have you taken? "); creditHours = scan.nextInt(); System.out.print("How many grade points have you earned? "); gradePoints = scan.nextDouble(); gpa = gradePoints / creditHours; hoursLeft = HOURS_NEEDED - creditHours; System.out.printf("Your GPA is %.2f\n", gpa); if( gpa >= 3.7 ) System.out.println("Wow, you're a hard worker!"); System.out.printf("You need %d more hours to complete your degree.\n", hoursLeft); if( hoursLeft < 0 ) System.out.println("You can graduate!"); System.out.println("See your advisor to get graduation clearance!"); Indentation alone does not define a block. What does this do when hoursLeft == 20? PLU Computer Science 13

if( coldOutside ) { wearCoat(); } else { wearShorts(); false true } Is it cold outside? Wear shorts. Wear a coat. In general if( boolean expression ) statement or block else statement or block The " else " part is optional PLU Computer Science 14

if-else System.out.print("How many credit hours have you taken? "); creditHours = scan.nextInt(); System.out.print("How many grade points have you earned? "); gradePoints = scan.nextDouble(); if-else avoids division by zero and computing with invalid if( creditHours > 0 ) (negative) input. { gpa = gradePoints / creditHours; } else { gpa = 0.0; } System.out.printf("Your GPA is %.2f\n", gpa); PLU Computer Science 15

Practice Write an if statement to calculate quizAve ( sum divided by numQuizzes ) only if numQuizzes is greater than 0. PLU Computer Science 16

Practice Write an if statement to calculate quizAve ( sum divided by numQuizzes ) only if numQuizzes is greater than 0. if( numQuizzes > 0 ) { quizAve = sum / numQuizzes; } PLU Computer Science 17

Practice Write an if statement to calculate tax ( totalSales times TAX_RATE ) only if forProfit ( char ) is 'y'. PLU Computer Science 18

Practice Write an if statement to calculate tax ( totalSales times TAX_RATE ) only if forProfit ( char ) is 'y'. if( forProfit == 'y' ) { tax = totalSales * TAX_RATE; } PLU Computer Science 19

Practice Write an if-else statement to print "Go Swimming!" and set cost to $5 if the temperature ( temp ) is at least 80 degrees, otherwise print "Take a hike" and set cost to $0. PLU Computer Science 20

Practice Write an if-else statement to print "Go Swimming!" and set cost to $5 if the temperature ( temp ) is at least 80 degrees, otherwise print "Take a hike" and set cost to $0. if( temp >= 80 ) { System.out.println("Go Swimming!"); cost = 5.0; } else { System.out.println("Take a hike"); cost = 0.0; } PLU Computer Science 21

Practice: IfPractice.java Check the class website and Turn-in on next Monday! PLU Computer Science 22