Read this chapter, which reviews how computers make decisions using if statements. As you read this tutorial, you will understand that sometimes it is important to evaluate the value of an expression and perform a task if the value comes out to be true and another task if it is false. In particular, try the simulated program under the heading "Simulated Program" to see how a different response is presented to the user based on if a number is positive or negative.
Pay special attention to the "More Than One Statement per Branch" header to learn how the 'else' statement is used when there is more than one choice.
14. Using Boolean Expressions
Answer:
Expression Value Expression Value 25 == 25 true 25 != 25 false 25 <= 25 true 25 > 25 false 25 >= 25 true 25 = 25 illegal -5 < 7 true -305 <= 97 true
Using Boolean Expressions
In an if
statement, the true or false
of a boolean expression picks whether the true branch or the false branch is executed. Look at another story problem:
A store wants a program that calculates the tax on an item of clothing. An item that costs $100 or more has a 5% tax. An item that costs less than $100 is tax free. Write a program that asks for a price, then calculates and prints the tax, then prints the total cost.
Here is the program, not quite finished:
public class TaxProgram { public static void main (String[] args) { double price; double tax ; System.out.println("Enter the price:"); if ( ) else System.out.println("Item cost: " + price + " Tax: " + tax + " Total: " + (price+tax) ); } } |
Here are some program fragments to use in completing the program. Use your mouse to copy-and-paste them into the program.
tax = price * taxRate; Scanner scan = new Scanner( System.in );
price = scan.nextDouble(); final double taxRate = 0.05;
price >= 100.0 import java.util.Scanner;
tax = 0.0;
(Of course, it would be nice to copy the program to a file, enter your corrections and run the program.)
Question 14: