1. 1 Tirgul no. 2 Topics covered: H Reading Input from the user. H Printing Output to the user. H if - else statement and switch. H Boolean Operators. H Checking your input. H Logical Operators.

2. 2 Reading Input from the user H We leave the discussion of Input for later chapters H For now we will supply you with classes for getting input in all exercises and examples.  The class called EasyInput allows you to read input from the user. H In order to read an integer/double we use EasyInput as follows: int numberOfItems = EasyInput.readInt(); double width = EasyInput.readDouble();

3. 3 Reading Input (contd.) H Please note that EasyInput is not a core Java class. We have supplied it for simplicity. H The EasyInput api is supplied on the course site.

4. 4 Example - Multiplying two numbers // Requests two integers and prints their // multiplication. class MultiplicationExample { public static void main(String[] args) { int a,b; int mul; System.out.print(“The first number: “); a = EasyInput.readInt(); System.out.print(“The second number: “); b = EasyInput.readInt(); mul = a * b; System.out.println(“The multiplication is” + mul); }

5. 5 Example: Circle area and circumference // Reads the radius of a circle and prints // its circumference and area to an output window class CircleExample { static final double PI = 3.1415927; public static void main(String[] args) { double r, circumference, area; System.out.print(“Enter radius: “); r = EasyInput.readDouble(); circumference = 2*PI*r; area = PI*r*r; System.out.print(“Circumference: “); System.out.println(circumference); System.out.print(“Area: “); System.out.println(area); }

6. 6 The if Statement H The Java if statement has the following syntax: if (boolean-condition) statement; H If the Boolean condition is true, the statement is executed; if it is false, the statement is skipped H This provides basic decision making capabilities

7. 7 Temperature class Temperature { static final int THRESHOLD = 65; public static void main(String[] args) { System.out.print(“Enter the temperature:”); int temperature = EasyInput.readInt(); System.out.println(“Current temperature “+ temperature); if (temperature < THRESHOLD) System.out.println(“It’s cold in here!”); }

8. 8 Boolean Expressions  The condition of an if statement must evaluate to a true or false result H Java has several equality and relational operators: Operator == != < <= > >= Meaning equal to not equal to less than less than or equal to greater than greater than or equal to

9. 9 Block Statements H Several statements can be grouped together into a block statement H Blocks are delimited by braces H A block statement can be used wherever a statement is called for in the Java syntax  See Temperature2.java

10. 10 Example - Temperature2 class Temperature2 { static final int THRESHOLD = 65; public static void main(String[] args) { System.out.print(“Enter the temperature: ”); int temperature = EasyInput.readInt(); System.out.println(“Current temperature “+ temperature); if (temperature < THRESHOLD) { System.out.println(“It’s cold in here!”); System.out.println(“But we’ll survive.”); }

11. 11 If.. Else Statement  An else clause can be added to an if statement to make it an if-else statement: if (condition) statement1; else statement2; H If the condition is true, statement1 is executed; if the condition is false, statement2 is executed  See Temperature3.java.

12. 12 Example - Temperature3 class Temperature3 { static final int FREEZING_POINT = 32; public static void main(String[] args) { System.out.print(“Enter the temperature: ”); int temperature = EasyInput.readInt(); if (temperature <= FREEZING_POINT) System.out.println(“It’s freezing!”); else System.out.println(“Above freezing.”); }

13. 13 Checking your Input H When requesting input from the user, you keep in mind that the input may be invalid. One way to handle this is to use if – else control statement: //number of items should be positive int numberOfItems = EasyInput.readInt(); if (numberOfItems < 0) { System.out.println( “Number of items must be positive!”); } else { double price = numberOfItems * ITEM_PRICE; System.out.print(“The total price is:“); System.out.println(price); }

14. 14 Logical Operators H There are three logical operators in Java: H They all take boolean operands and produce boolean results H Logical NOT is unary (one operand), but logical AND and OR are binary (two operands) Operator ! && || Operation Logical NOT Logical AND Logical OR

15. 15 Logical NOT H The logical NOT is also called logical negation or logical complement  If a is true, !a is false; if a is false, then !a is true H Logical expressions can be shown using truth tables a false true !a true false

16. 16 Logical AND  The expression a && b is true if both a and b are true, and false otherwise H Truth tables show all possible combinations of all terms a false true b false true false true a && b false true

17. 17 Logical OR  The expression a || b is true if a or b or both are true, and false otherwise a false true b false true false true a || b false true

18. 18 Logical Operators H Logical operators are used to form more complex logical expressions if (a<1 || a%2!=0) { System.out.println( “The input should be a positive “+ “even number!”); return; } H Logical operators have precedence relationships between themselves and other operators

19. 19 Logical Operators H Full expressions can be evaluated using truth tables a < 1 false true a%2!=0 false true false true a<1 || a%2!=0 false true

20. 20 Nested If // Receives 2 integers and compares them class CompareExample { public static void main(String[] args) { System.out.print(“First number: ); int a = EasyInput.readInt(); System.out.print(“Second number: ); int b = EasyInput.readInt(); if (a != b) if (a > b) System.out.println(a+” is greater”); else System.out.println(b+” is greater”); else System.out.println(“the numbers are equal”); }

21. 21 Switch Construct Switch( integral expression) { case integral-value1: statements; break; case integral-value2: statements; break; : case integral-valueN: statements; break; default: statements; break; }

22. 22 Switch Construct (cont.) Switch( integral expression) { case integral-value1: case integral-value2: statements; break; : case integral-valueN: statements; break; default: statements; break; }

23. 23 public class Schedule { public final int SUNDAY = 1; public final int MONDAY = 2; public final int TUESDAY = 3; public void printSchedule(int day) { System.out.println(“Schedule for today is:”); switch(day) { case SUNDAY: System.out.println(“10:00 - 12:00 : Infi”); System.out.println(“12:00 - 14:00 : Alg”); break; case MONDAY: case TUESDAY: System.out.println(“10:00 - 13:00 discrete math”); break; default: System.out.println(“Error: No such day”); break; }