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Lecture 3 Decisions (Conditionals). 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 .
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Lecture 3 Decisions (Conditionals)
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.
Alternative Paths of Execution false radius < 0 true area = radius * radius * PI "Area is" + area "Incorrect input"
One-Way if Statements false conditional if (conditional) do something; do next thing; true do something do next thing
Two-Way if Statements false conditional if (conditional) do something; do next thing; true do something do other thing do next thing
if-else if-else false false conditional 1 conditional 2 true true yet another thing do something do other thing if (condition 1) do something; else if (condition 2) do other thing; else yet another thing; do next thing; do next thing
import java.util.Scanner;publicclass LetterGradeDemo{publicstaticvoid 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'; }elseif (avg >= 80.0) { grade = 'B'; }elseif (avg >= 70.0) { grade = 'C'; }elseif (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); }}
Switch Statements case 0 stuff break case 0: case 1 stuff break case 1: case 2 stuff break case 2: default stuff default:
Switch Statement Rules (andStringtypes starting with JDK 7)
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.
Formatting Console Output specifying display data types
Formatting Console Output specifying width and precision
