1. Lecture 3 Decisions (Conditionals)

2. One of the essential features of computer programs is their ability to make decisions. Like a train that changes tracks depending on how the switches are set, a program can take different actions depending on inputs and other circumstances. In this chapter, you will learn how to program simple and complex decisions. You will apply what you learn to the task of checking user input.

3. radius < 0 "Incorrect input" area = radius * radius * PI "Area is" + area Alternative Paths of Execution true false

4. Comparison Operators

5. conditional do something true false do next thing if (conditional) do something; do next thing; One-Way if Statements

6. if (conditional) do something; do next thing; conditional do something true false do next thing do other thing Two-Way if Statements

7. conditional 1 do something true false do next thing do other thing conditional 2 true false yet another thing if (condition 1) do something; else if (condition 2) do other thing; else yet another thing; do next thing; if-else

8. Example Program

9. import java.util.Scanner; public class LetterGradeDemo { public static void main(String[] args) { Scanner input = new Scanner(System.in); System.out.print("Enter final average (0-100)... "); double avg = input.nextDouble(); char grade; if (avg >= 90.0) { grade = 'A'; } else if (avg >= 80.0) { grade = 'B'; } else if (avg >= 70.0) { grade = 'C'; } else if (avg >= 60.0) { grade = 'D'; } else { grade = 'F'; } if(grade == 'A') System.out.println("An average of " + avg + " is an " + grade); else System.out.println("An average of " + avg + " is a " + grade); } }

10. Boolean Operators

11. Example Program

12. case 0: case 0 stuffbreak case 1: case 2: default: case 1 stuff case 2 stuff default stuff break Switch Statements

13. Switch Statement Rules ( and String types starting with JDK 7 )

14. Alternative Form for Conditional Statements For both version of the conditional constructs below, if x is greater than 0 then y is assigned the value 1, otherwise y is assign the value -1. This alternative version of the two-way conditional statement will not be used in this course. It is provided here for purposes of comparison and the understanding of java programs written by others.

15. Formatting Console Output specifying display data types

16. Formatting Console Output specifying width and precision

17. Operator Precedence

18. Confirmation Dialogs

19. Summary