9/6: Variable Types, Arithmetic Operators, Comparison Operators Addition.java in depth Variable types & data types Input from user: how to get it Arithmetic operators

Addition.java import javax.swing.JOptionPane; public class Addition { public static void main ( String args[] ) { String firstNumber, secondNumber; int number1, number2, sum; firstNumber = JOptionPane.showInputDialog ( "Enter a number" ); secondNumber = JOptionPane.showInputDialog ( "And another" ); number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber ); sum = number1 + number2; JOptionPane.showMessageDialog ( null, "The sum is " + sum, "Results", JOptionPane.PLAIN_MESSAGE ); System.exit ( 0 ); } import statement class header method header declaring variables: Strings & ints

Variables & Data Types String – a series of characters. –EX: Ann, 1450, var30, g, YES –to declare a String variable, put the variable type String before the name of the variable. String firstNumber ; –to declare more than one String variable at the same time, separate the variable names with commas. String firstNumber, secondNumber ; A declaration is a statement – must end with a semicolon.

Variables & Data Types int – an integer-type number. –EX: 45, -1001, 3, –to declare an int variable, put the variable type int before the name of the variable. int number1 ; –to declare more than one int variable at the same time, separate the variable names with commas. int number1, number2 ; –other number formats: float, double, long, short

Addition.java import javax.swing.JOptionPane; public class Addition { public static void main ( String args[] ) { String firstNumber, secondNumber; int number1, number2, sum; firstNumber = JOptionPane.showInputDialog ( "Enter a number" ); secondNumber = JOptionPane.showInputDialog ( "And another" ); number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber ); sum = number1 + number2; JOptionPane.showMessageDialog ( null, "The sum is " + sum, "Results", JOptionPane.PLAIN_MESSAGE ); System.exit ( 0 ); } initializing firstNumber & secondNumber

Inputs: How we did it. We initialized (gave an initial value to) firstNumber & secondNumber by the lines firstNumber = JOptionPane.showInputDialog ( "Enter a number" ); secondNumber = JOptionPane.showInputDialog ( "And another" ); JOptionPane.showInputDialog panes accept String type inputs. Even if it looks like a number, Java sees it as a String.

Addition.java import javax.swing.JOptionPane; public class Addition { public static void main ( String args[] ) { String firstNumber, secondNumber; int number1, number2, sum; firstNumber = JOptionPane.showInputDialog ( "Enter a number" ); secondNumber = JOptionPane.showInputDialog ( "And another" ); number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber ); sum = number1 + number2; JOptionPane.showMessageDialog ( null, "The sum is " + sum, "Results", JOptionPane.PLAIN_MESSAGE ); System.exit ( 0 ); } initializing number1 & number2

Inputs: How we did it. We then initialized (gave an initial value to) number1 & number2 by the lines number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber ); These lines convert the String values of firstNumber and secondNumber into int values and store them as number1 and number2.

Addition.java import javax.swing.JOptionPane; public class Addition { public static void main ( String args[] ) { String firstNumber, secondNumber; int number1, number2, sum; firstNumber = JOptionPane.showInputDialog ( "Enter a number" ); secondNumber = JOptionPane.showInputDialog ( "And another" ); number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber ); sum = number1 + number2; JOptionPane.showMessageDialog ( null, "The sum is " + sum, "Results", JOptionPane.PLAIN_MESSAGE ); System.exit ( 0 ); } initializing sum

Arithmetic Operators

Order of Operation Just like algebra inside parentheses first multiplication, division, & modulus next addition & subtraction last left to right EX: 2 * % 2 - (4 / ) = ?

Order of Operation Example 2 * % 2 - (4 / ) = ? 2 * % 2 - ( ) = ? 2 * % 2 - ( 7 ) = ? % 2 - ( 7 ) = ? ( 7 ) = ? = 2

1 st Program of the Day: pg. 58 Pg. 58: Comparison.java –Pay attention to the comparison operators ( =, etc.) Second Half: –Comparison.java in depth: –the if structure –comparison operators –assigning new values to an old variable.

Part 2: Comparison Operators Comparison.java Using the if structure Equality operators Relational operators

Comparison.java import javax.swing.JOptionPane; public class Comparison { public static void main( String args[] ) { String firstNumber, secondNumber, result; int number1, number2; firstNumber = JOptionPane.showInputDialog( "Enter first int.:" ); secondNumber = JOptionPane.showInputDialog( "Enter 2nd int:" ); number1 = Integer.parseInt( firstNumber ); number2 = Integer.parseInt( secondNumber ); result = ""; import statement class header method header declaring variables: Strings & ints initializing firstNumber & secondNumber initializing number1 & number2 initializing result

Comparison.java (pt. 2) if ( number1 == number2 ) result = number1 + " == " + number2; if ( number1 != number2 ) result = number1 + " != " + number2; if ( number1 < number2 ) result = result + "\n" + number1 + " < " + number2; if ( number1 > number2 ) result = result + "\n" + number1 + " > " + number2; if ( number1 <= number2 ) result = result + "\n" + number1 + " <= " + number2; if ( number1 >= number2 ) result = result + "\n" + number1 + " >= " + number2; “If number1 is equal to number2, then set result to be number1 plus a double equal sign plus number2.”

The if structure Use the if structure to have statements execute ONLY under certain conditions. if ( condition ) rest of statement ; Note that the if ( condition ) is not a statement by itself ( just like English ). The spacing and line structure is good practice.

Comparison.java (pt. 2) if ( number1 == number2 ) result = number1 + " == " + number2; if ( number1 != number2 ) result = number1 + " != " + number2; if ( number1 < number2 ) result = result + "\n" + number1 + " < " + number2; if ( number1 > number2 ) result = result + "\n" + number1 + " > " + number2; if ( number1 <= number2 ) result = result + "\n" + number1 + " <= " + number2; if ( number1 >= number2 ) result = result + "\n" + number1 + " >= " + number2; “If number1 is less than number2, set result to be itself plus a new line escape sequence plus number1 plus a ‘less than’ sign plus number2.”

Equality & Relational Operators To compare values. Equality operators: Equal to, not equal to Relational operators: Greater than, less than

Equality Operators

Relational Operators

Comparison.java (pt. 3) JOptionPane.showMessageDialog( null, result, "Comparison Results", JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); } result, whatever it is after executing the if statements, is put in the main body of the MessageDialog box.

Program of the Day Problem 2.17 (pg. 73): write a program Work in pairs Use Comparison.java as a help/template in creating the program