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7/6: Inputs, Variable Types, etc.

7/6: Inputs, Variable Types, etc. Addition.java in depth Variable Types & data types Input from user: how to get it Arithmetic operators. import statement. class header. method header. declaring variables: Strings & ints. Addition.java. import javax.swing.JOptionPane;

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7/6: Inputs, Variable Types, etc.

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  1. 7/6: Inputs, Variable Types, etc. • Addition.java in depth • Variable Types & data types • Input from user: how to get it • Arithmetic operators

  2. import statement classheader method header declaring variables: Strings& ints 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 ); } }

  3. 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.

  4. Variables & Data Types • int – an integer-type number. • EX: 45 , -1001 , 3 , 58692 • 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

  5. initializing firstNumber &secondNumber 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 ); } }

  6. 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.

  7. initializing number1 &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 ); } }

  8. 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.

  9. initializing sum 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 ); } }

  10. Arithmetic Operators

  11. Order of Operation • Just like algebra • inside parentheses first • multiplication, division, & modulus next • addition & subtraction last • left to right • EX: 2 * 4 + 3 % 2 - (4 / 2 + 5 ) = ?

  12. Order of Operation Example • 2 * 4 + 3 % 2 - (4 / 2 + 5 ) = ? • 2 * 4 + 3 % 2 - ( 2 + 5 ) = ? • 2 * 4 + 3 % 2 - ( 2+ 5 ) = ? • 2 * 4 + 3 % 2 - ( 7 ) = ? • 2 * 4 + 3 % 2 - ( 7 ) = ? • 8 + 3 % 2 - ( 7 ) = ? • 8 + 3 % 2 - ( 7 ) = ? • 8 + 1 - ( 7 ) = ? • 8 + 1 - 7 = 2

  13. Program of the Day: pg. 58 • Pg. 58: Comparison.java • Pay attention to the comparison operators (<, >=, etc.) • Next time: • Comparison.java in depth: • the if structure • comparison operators • assigning new values to an old variable.

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