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1/28: Inputs, Variable Types, etc. • • • • Addition.java in depth Variable types & data types Input from user: how to get it Arithmetic operators Addition.java //Fig. 2.9: Addition.java //An addition program import //Java extension packages statement import javax.swing.JOptionPane; //import class JOptionPane class header public class Addition { method header //main method begins execution of Java application public static void main ( String args[] ) declaring { variables: String firstNumber; // first String entered by user Strings String secondNumber; // second String entered by user & ints int number1; // first number to add int number 2; // second number to add int sum; // sum of number1 & number2 //read in first number from user as a String firstNumber = JOptionPane.showInputDialog ( "Enter first integer" ); Addition.java //read in second number from user as a String secondNumber = JOptionPane.showInputDialog ( “Enter second integer" ); //convert numbers from type String to type int number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber ); //add the numbers, assign the value to sum sum = number1 + number2; //display the results JOptionPane.showMessageDialog ( null, “The sum is " + sum, "Results", JOptionPane.PLAIN_MESSAGE ); System.exit ( 0 ); } //end method main } //end class Addition //terminate the application if no errors 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 , 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 Addition.java //Fig. 2.9: Addition.java //An addition program //Java extension packages import javax.swing.JOptionPane; //import class JOptionPane public class Addition { //main method begins execution of Java application public static void main ( String args[] ) { String firstNumber; // first String entered by user String secondNumber; // second String entered by user int number1; // first number to add int number 2; // second number to add int sum; // sum of number1 & number2 initializing firstNumber //read in first number from user as a String firstNumber = JOptionPane.showInputDialog ( "Enter first integer" ); Addition.java initializing //read in second number from user as a String secondNumber secondNumber = JOptionPane.showInputDialog ( “Enter second integer" ); //convert numbers from type String to type int number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber ); //add the numbers, assign the value to sum sum = number1 + number2; //display the results JOptionPane.showMessageDialog ( null, “The sum is " + sum, "Results", JOptionPane.PLAIN_MESSAGE ); System.exit ( 0 ); } //end method main } //end class Addition //terminate the application if no errors 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 //read in second number from user as a String secondNumber = JOptionPane.showInputDialog ( “Enter second integer" ); initializing number1 & number2 //convert numbers from type String to type int number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber ); //add the numbers, assign the value to sum sum = number1 + number2; //display the results JOptionPane.showMessageDialog ( null, “The sum is " + sum, "Results", JOptionPane.PLAIN_MESSAGE ); System.exit ( 0 ); } //end method main } //end class Addition //terminate the application if no errors 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 //read in second number from user as a String secondNumber = JOptionPane.showInputDialog ( “Enter second integer" ); //convert numbers from type String to type int number1 = Integer.parseInt ( firstNumber ); number2 = Integer.parseInt ( secondNumber ); //add the numbers, assign the value to sum initializing sum = number1 + number2; sum //display the results JOptionPane.showMessageDialog ( null, “The sum is " + sum, "Results", JOptionPane.PLAIN_MESSAGE ); System.exit ( 0 ); } //end method main } //end class Addition //terminate the application if no errors Arithmetic Operators Java operator Arithmetic operator Addition + Algebraic expression Java expression f+7 f+7 Subtraction - p–c p–c Multiplication * pv p*v Division / x/y x/y Modulus % r mod s r%s 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 ) = ? 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 Program of the Day: pg. 81 • Pg. 81: 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.