Tirgul no. 2

1
Tirgul no. 2

• Topics covered
• Reading Input from the user.
• Printing Output to the user.
• if - else statement and switch.
• Boolean Operators.
• Checking your input.
• Logical Operators.

2
Reading Input from the user

• We leave the discussion of Input for later
  chapters
• 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.
• In order to read an integer/double we use
  EasyInput as follows
• int numberOfItems EasyInput.readInt()
• double width EasyInput.readDouble()

3
Reading Input (contd.)

• Please note that EasyInput is not a core Java
  class. We have supplied it for simplicity.
• The EasyInput api is supplied on the course site.

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
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 2PIr
• area PIrr
• System.out.print(Circumference )
• System.out.println(circumference)
• System.out.print(Area )
• System.out.println(area)

6
The if Statement

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

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 lt THRESHOLD)
• System.out.println(Its cold in
  here!)

8
Boolean Expressions

• The condition of an if statement must evaluate to
  a true or false result
• Java has several equality and relational
  operators

Operator ! lt lt gt gt
Meaning equal to not equal to less than less
than or equal to greater than greater than or
equal to
9
Block Statements

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

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 lt THRESHOLD)
• System.out.println(Its cold in
  here!)
• System.out.println(But well
  survive.)

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
• If the condition is true, statement1 is executed
  if the condition is false, statement2 is
  executed
• See Temperature3.java.

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 lt FREEZING_POINT)
• System.out.println(Its freezing!)
• else
• System.out.println(Above
  freezing.)

13
Checking your Input

• 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 lt 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
Logical Operators

• There are three logical operators in Java
• They all take boolean operands and produce
  boolean results
• Logical NOT is unary (one operand), but logical
  AND and OR are binary (two operands)

15
Logical NOT

• 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
• Logical expressions can be shown using truth
  tables

16
Logical AND

• The expression a b is true if both a and b are
  true, and false otherwise
• Truth tables show all possible combinations of
  all terms

17
Logical OR

• The expression a b is true if a or b or both
  are true, and false otherwise

18
Logical Operators

• Logical operators are used to form more complex
  logical expressions
• if (alt1 a2!0)
• System.out.println(
• The input should be a positive
• even number!)
• return
• Logical operators have precedence relationships
  between themselves and other operators

19
Logical Operators

• Full expressions can be evaluated using truth
  tables

alt1 a2!0 false true true true
a lt 1 false false true true
a2!0 false true false true
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 gt b)
• System.out.println(a is
  greater)
• else
• System.out.println(b is
  greater)
• else
• System.out.println(the numbers are
  equal)

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
Switch Construct (cont.)
Switch( integral expression) case
integral-value1 case integral-value2
statements break
case integral-valueN statements
break default statements
break
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(S
chedule for today is) switch(day)
case SUNDAY System.out.println(1000 -
1200 Infi) System.out.println(1200 -
1400 Alg) break case MONDAY
case TUESDAY System.out.println(1000 -
1300 discrete math) break default
System.out.println(Error No such day)
break