CS177 Week2: Recitation Primitive data types and Strings with code examples

Questions?

Data Types

int  int x; //declaration of variable x  x = 23; //assigns the number 23 to x  Stored as 1’s and 0’s. 23d = 10111b.  d stands for decimal, b for binary

Binary -> Decimal Conversion  What does b equal in decimal?

222

Decimal -> Binary Conversion  Do the following steps:  Start with a decimal number x  Set binary number b = 0  Until x = 0  Is x odd?  If yes, put a 1 at the end of b  If no, put a 0 at the end of b  Divide x by 2, rounding down (truncation)  Reverse the digits of b

Ex: x = 9

Ex: x = b = 222d, just like before

Positive and Negative Numbers  Positive numbers start with a 0 bit  Negative numbers start with a 1 bit  2’s complement – way that a negative number is represented

Doubles  Rational numbers (can still be an integer, but it is stored differently)  64 bits  double y = 1.25; //declares double y and assigns 1.25 to y  double z = 3;  double a = 2.0;  double b = -8.8;

Loosely typed or strongly typed?  Java is:  Strongly typed  double x;  x = 3;  What is the type of variable x?  A double!

Strings  Many letters in one type  String word1 = “purdue”;  String word2 = “boilermakers”;  String word3 = “p”;  String word4 = “”; //This is legal – called empty String

Chars  char – one character. Could be any ASCII character  String – many characters together  char w = ‘a’;  char x = w;  char y = ‘w’;  String z = “w”;  Are the variables w and x equal?  Are the variables x and y equal?  Are the variables y and z equal?

String - String concatenation /************************************************************************* * Compilation: javac Ruler.java * Execution: java Ruler * * Prints the relative lengths of the subdivisions on a ruler. * * % java Ruler * 1 * * * * * *************************************************************************/

public class Ruler { public static void main(String[] args) { String ruler1 = "1 "; String ruler2 = ruler1 + "2 " + ruler1; String ruler3 = ruler2 + "3 " + ruler2; String ruler4 = ruler3 + "4 " + ruler3; String ruler5 = ruler4 + "5 " + ruler4; System.out.println(ruler1); System.out.println(ruler2); System.out.println(ruler3); System.out.println(ruler4); System.out.println(ruler5); }

Double Operation - Quadratic formula /************************************************************************* * Compilation: javac Quadratic.java * Execution: java Quadatic b c * Given b and c, solves for the roots of x*x + b*x + c. * Assumes both roots are real valued. * % java Quadratic * 2.0 * 1.0 * % java Quadratic * * * * Remark: is the golden ratio. * * % java Quadratic * NaN *************************************************************************/

public class Quadratic { public static void main(String[] args) { double b = Double.parseDouble(args[0]); double c = Double.parseDouble(args[1]); double discriminant = b*b - 4.0*c; double sqroot = Math.sqrt(discriminant); double root1 = (-b + sqroot) / 2.0; double root2 = (-b - sqroot) / 2.0; System.out.println(root1); System.out.println(root2); }

Char Operation /************************************************************************* * Compilation: javac Charactertest.java * Execution: java Charactertest Is this letter lowercase? true Is this letter uppercase? false Is this a letter? true /************************************************************************* public class Charactertest { public static void main(String args[]) { char letter = 'd'; boolean lowerCase = Character.isLowerCase(letter); boolean upperCase = Character.isUpperCase(letter); boolean letterOrdigit = Character.isLetter(letter); System.out.println("Is this letter lowercase? " + lowerCase); System.out.println("Is this letter uppercase? " + upperCase); System.out.println("Is this a letter? " + letterOrdigit); }

Questions?