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

PLU Computer Science

CSCI 144 - Introduction to Computer Science

Instructor: John Goettsche Computer Science Department Pacific Lutheran University Fall 2017

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Before class

• Quiz on Monday
• Turn-in Buggy codes
• Solutions to Buggy codes
• CAT QA

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Boolean Expressions and If Statements

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Sequential Execution

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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); System.out.printf("You need %d more hours", hoursLeft); System.out.println(" to complete your degree."); Execution flow

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Wear a coat. true Is it cold

• utside?

Conditional Execution Java code

if( coldOutside ) wearCoat(); false

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Wear a coat. true Is it cold

• utside?

Wear a hat. Wear gloves. if( coldOutside ) { wearCoat(); wearHat(); wearGloves(); } Curly braces define a block of statements. false

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Statement

• r

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

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Think/Pair/Share

Write down at least two instances where you might have used a conditional in one of your previous lab assignments

• r pair exercises.

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Relational Operators

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Boolean Operators

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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

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Boolean Expressions

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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?

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GPA Example with Conditional Execution

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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!"); }

Note the use of indentation and curly braces.

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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?

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Wear a coat. true Is it cold

• utside?

Wear shorts. false

if( coldOutside ) { wearCoat(); } else { wearShorts(); } if( boolean expression ) statement or block else statement or block In general The "else" part is

• ptional

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if-else

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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( creditHours > 0 ) { gpa = gradePoints / creditHours; } else { gpa = 0.0; } System.out.printf("Your GPA is %.2f\n", gpa); if-else avoids division by zero and computing with invalid (negative) input.

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Practice

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Write an if statement to calculate quizAve (sum divided by numQuizzes) only if numQuizzes is greater than 0.

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Practice

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if( numQuizzes > 0 ) { quizAve = sum / numQuizzes; }

Write an if statement to calculate quizAve (sum divided by numQuizzes) only if numQuizzes is greater than 0.

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Practice

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Write an if statement to calculate tax (totalSales times TAX_RATE) only if forProfit (char) is 'y'.

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Practice

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if( forProfit == 'y' ) { tax = totalSales * TAX_RATE; }

Write an if statement to calculate tax (totalSales times TAX_RATE) only if forProfit (char) is 'y'.

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Practice

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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.

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Practice

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if( temp >= 80 ) { System.out.println("Go Swimming!"); cost = 5.0; } else { System.out.println("Take a hike"); cost = 0.0; }

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.

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

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