#### Transcript Boolean expressions, part 1: Compare operators

Boolean expressions, part 1: Compare operators Compare operators • Compare operators • Compare operators compare 2 numerical values and return a Boolean (logical) value • A compare operator will return the value true if the test is successful A compare operator will return the value false if the test is unsuccessful Compare operators (cont.) • Compare operators in Java: Operator symbol Example Meaning < a<b Returns true if a < b, otherwise returns false <= a <= b Returns true if a ≤ b, otherwise returns false > a>b Returns true if a > b, otherwise returns false >= a >= b Returns true if a ≥ b, otherwise returns false == a == b Returns true if a is not equal to b, otherwise returns false != a != b Returns true if a is not equal to b, otherwise returns false Example program: test divisibility • Problem description: • Write a Java program that reads in a number a and a number b • The program print a message when a is divisible by b • Algorithm: • A number a is divisible by the number b if and only if: •The remainder of the division a/b is equal to 0 Example program: test divisibility (cont.) • Java program: import java.util.Scanner; public class Divisible { public static void main(String[] args) { int a, b; Scanner in = new Scanner(System.in); // Construct Scanner object System.out.print("Enter a: "); a = in.nextInt(); // Read in number into a System.out.print("Enter b: "); b = in.nextInt(); // Read in number into b if ( (a % b) == 0 ) System.out.println(a + " is divisible by " + b); } } Example program: test divisibility (cont.) • Explanation: • The expression (a % b) == 0 will: 1. First compute the remainder of the division a/b 2. Then compare the result (i.e., the remainder of the division) to the value 0 Example program: test divisibility (cont.) • Example Program: (Demo above code) – Prog file: http://mathcs.emory.edu/~cheung/Courses/170/Syllabus/06/Progs/ Divisible01.java • How to run the program: • Right click on link and save in a scratch directory • To compile: javac Divisible01.java • To run: java Divisible01 Comparing integer and floating point values • Automatic conversion rule for compare operators: • The same automatic conversion rules used for arithmetic operators apply for compare operators • The automatic conversion rules for arithmetic operators were summarized on this webpage: http://mathcs.emory.edu/~cheung/Courses/170/S yllabus/04/conversion.html Priority of the compare operators • For practical purposes, you can assume that: • All compare operators have the same priority This is because you cannot have back to back compare operations Example: this is illegal a < b == c Because you cannot have back to back compare operations, there is no need to decide which one has higher priority. Priority of the compare operators (cont.) • Priority ranking of the compare operators against the previously discussed operators: Priority level Operator(s) Description Associativity 1 () Brackets 2 (int) − Casting, negation 3 ++, -- Increment, decrement 4 * / % Multiple, divide, remainder Left to right 5 + - Add, subtract Left to right 6 < <= > >= == != Compare operators 7 = += -= ... Assignment operators Right to left Right to left Priority of the compare operators (cont.) • Reference: http://introcs.cs.princeton.edu/java/11precedence/ Priority of the compare operators (cont.) • Example 1: boolean a; Statement: a = 3 > 1; Operators in statement: = > Executed as follows: a = 3 > 1; // > has higher priority than = a = true; Priority of the compare operators (cont.) • Example 2: boolean a; Statement: a = 3 + 4 <= 5 - 2; Operators in statement: = + <= Executed as follows: a = 3 + 4 <= 5 - 2; // + and - has highest priority a = 7 <= 3; a = true; // <= has higher priority than =