CS 177 Week 3 Recitation Slides Basic Math Operations, Booleans, and Character Operations

Announcements Project 1 is posted this morning. It is due on Sep. 24th 9pm TAs will start consulting hours next week Mon-Thu 6:00pm to 9:00 pm Mentor Program available Wed 5:30pm to 7:30pm in LWSN B158 Bonus points 5% extra for total score

QUESTIONS???

Basic Operations Recap

Operations On Integers +, -, *, / Addition, subtraction, multiplication and division Note that division of integers drops the fractional part +=, -=, *=, /= a += 4;  a = a + 4; c *= 5;  c = c * 5; ++, -- a ++;  a = a + 1; % Remainder of division a = 10 % 3; // a contains 1 b -= 3;  b = b - 3; d /= 2;  b = b / 2; b --;  b = b - 1;

Question What are the ways we can write to increment variable a by 1? a = a + 1; a += 1; a ++;

Basic Operations w/Integers Code Example 1 public class IntegerOperations { public static void main(String[] args) { int a; int b; a = 13 + 20; // a contains 33 b = a / 11; // b contains 3 System.out.println("a = " + a); System.out.println("b = " + b); a -= 7; b = a / b; // Result = 8.66 but int type means 8 b++; // Increment b from 8 to 9 } Output a = 33 b = 3 a = 26 b = 9

Basic Operations On Doubles Same operations as integers But the fractional part is retained

Basic Operations w/Doubles Code Example 1 public class DoubleOperations { public static void main(String[] args) double a; double b; double c; double d; a = 4.0 / 3.0; b = a - 1; c = b + b + b * 2; d = 9 / 4; d--; System.out.println("a = " + a); System.out.println("b = " + b); System.out.println("c = " + c); System.out.println("d = " + d); } Output a = 1.3333333333333333 b = 0.3333333333333333 c = 1.3333333333333333 d = 1.0 Question Variable d is a double or an integer?

Casting in Java int a = (int) 1.8; // convert double 1.8 into an int 1 Convert one data type to another loss of precision float  int, number is rounded down Let the Java compiler know that you are aware that you are going to lose some information, but you are ok with that.

Math Library in Java Java contains a Math class that includes a variety of math functions that can be used to perform other operations on integers and/or doubles The term “library” just means that it is a collection of predefined methods/functions that a programmer can leverage Brief example: double x = 16.0; double y; y = Math.sqrt(x); // y will be 4.0 after this line executes

Math Library in Java Return type Name Job double sin( double theta ) Find the sine of angle theta cos( double theta ) Find the cosine of angle theta tan( double theta ) Find the tangent of angle theta exp( double a ) Raise e to the power of a (ea) log( double a ) Find the natural log of a pow( double a, double b ) Raise a to the power of b (ab) long round( double a ) Round a to the nearest integer random() Create a random number in [0, 1) sqrt( double a ) Find the square root of a

Math Operations Code Example public class MathOperations { public static void main(String[] args) { double a = 25; double b = 4; double x = 2.0; double y = 6.731; double z = 0.5; a = Math.sqrt(a); b = Math.pow(b, 2); x = Math.pow(x, 5) / 8; y = Math.round(y); z = Math.cos(z); System.out.println("a is " + a); System.out.println("b is " + b); System.out.println("x is " + x); System.out.println("y is " + y); System.out.println("z is " + z); } Output a is 5.0 b is 16.0 x is 4.0 y is 7.0 z is 0.8775825618903728 Note Math.round(y); (int) (y + 0.5); These are the same.

Boolean Operations Operator Symbol Function NOT ! true  false , false  true AND && Outputs true only if both operands are true OR || Outputs true if either or both operands are true XOR ^ Outputs true if one but not both operands are true

Boolean Operations Code Example Output NOT true is false NOT false is true true AND false is false true OR false is true true XOR false is true true AND true is true true XOR true is false public class BooleanOperations { public static void main(String[] args) { boolean test1 = true; boolean test2 = false; boolean test3 = test1 && test2; boolean test4 = test1 || test2; boolean test5 = test1 ^ test2; boolean test6 = test1 && test1; boolean test7 = test1 ^ test1; System.out.println("NOT " + test1 + " is " + !test1); System.out.println("NOT " + test2 + " is " + !test2); System.out.println(test1 + " AND " + test2 + " is " + test3); System.out.println(test1 + " OR " + test2 + " is " + test4); System.out.println(test1 + " XOR " + test2 + " is " + test5); System.out.println(test1 + " AND " + test1 + " is " + test6); System.out.println(test1 + " XOR " + test1 + " is " + test7); }

Characters in Java A digit, a letter or a symbol number char A digit, a letter or a symbol Denoted by single quotes in Java ‘T’, ‘@’, ‘2’ Represented by numbers in computer Char ch = ‘T’; // ch contains integer 84 // ch contains character ‘T’ Escape sequences \ single quote ‘\’’ New line ‘\n’ Tab ‘\t’ Back slash ‘\\’

Character Operations Characters are actually integers ASCII number change. Become another character. char ch = ‘a’ + 2; // ch contains number 99 representing ‘c’ ch += 3; // ch contains number 102 representing ‘f’ int dis = ‘g’ – ‘c’; // dis contains 4, no cast required

Character Operations Code Example public class CharacterOperations { public static void main(String[] args) { char letter; int number; letter = ‘l'; // letter contains ‘l' letter++; // letter contains ‘m' System.out.println("letter = '" + letter + "'"); number = letter; // no cast required System.out.println("number = " + number); letter = ‘h'; number = letter - 'a' + 1; System.out.println("'" + letter + "' is the " + number + "th letter of the alphabet"); } Output letter = 'm' number = 109 'h' is the 8th letter of the alphabet

Strings in Java A list of characters Denoted by double quotes String str = “Computer”; +, += operators : concatenation String str1 = “Java is”; String str2 = str1 + “ programming language.”; str1 += “ a cup of coffee.”; Can concatenate variables of other types as text strings int a = 1; int b = 3; int c = a + b; String str3 = a + “ + “ + b + “ = “ + c;

String Class The String class contains several methods that can be used to perform operations on a string. Method Name Return Type Description Usage compareTo(String t) int Compares two strings string1.compareTo(string2); length() Gets length of string string1.length(); charAt(int i) char Finds ith character string1.charAt(3); equals(String t) Boolean Are two strings equal? string1.equals(string2); substring(int i, int j) String Finds substring from ith character to character before jth one String1.substring(0, 2)

Methods in String Class String str = “Boiler Up!”; Comparison int a = str.compareTo(“Purdue”); // a contains a negative number boolean b = str.equals(“Purdue”); // b contains false length() gives number of characters in the string int l = str.length(); // l contains 10

Methods in String Class String str = “Boiler Up!”; charAt(int i) get the character at position i char c = charAt(2); // index starts from 0, c contains ‘i’, not ‘o‘ substring(int i, int j) gives the substring from position i and to the position before j String str2 = str.substring(0, 6); // str2 contains “Boiler” String str3 = str.substring(7, str.length()); // str3 contains “Up!” 1 2 3 4 5 6 7 8 9 B o i l e r U p !

Strings Class Code Example public class StringOperations { public static void main(String[] args) { String word1; String word2; word1 = “chrome"; word2 = “home"; System.out.println(“Does " + word1 + " = " + word2 + "?"); System.out.println( word1.equals(word2) + "!"); System.out.println("The length of " + word2 + " is: " + word2.length() ); int position = 3; System.out.println("Position " + position + " in " + word2 + " is '" + word2.charAt(position) + "'"); word1 = "computers are cool"; word2 = word1.substring(3, 8); System.out.println(word2); } Output Is chrome the same as home? false! The length of home is: 4 Position 3 in home is 'e' puter

Question If we have String word1 = “Purdue”; String word2 = “Purdue”; This statement will return true or false? word1.equals(word2); What about this one? word1 == word2;

Wrapper Classes Each primitive data type in Java has a wrapper class Integer converts between int  String String  int String str = “345”; int a = Integer.parseInt(str); int  String int value = 890; String str = Integer.toString(value); Double is similar. double  String String  double: double d = Double.parseDouble(“345.12”); double  String : String str = Double.toString(3.14);

Wrapper Classes Character gives information about a particular char Remind from last week: boolean b = Character.isLowerCase(‘c’); b = Character.isUpperCase(‘c’); b = Character.isLetter(‘c’); b = Character.isDigit(‘c’);

Wrapper Classes Code Example 1 public class Wrappers { public static void main(String[] args) { String number1 = "666"; String number2 = "4.51"; int value1 = Integer.parseInt( number1 ); double value2 = Double.parseDouble( number2 ); System.out.println("The integer is " + value1); System.out.println("The double is " + value2); } What would happen if the parseInt and parseDouble methods were not used? (i.e.: int value1 = number1;) Output The integer is 666 The double is 4.51

Wrapper Classes Code Example 2 public class Wrappers { public static void main(String[] args) { char c = 'U'; char d = '4'; System.out.println(c + " is:"); System.out.println("a letter:\t" + Character.isLetter(c)); System.out.println("a digit:\t" + Character.isDigit(c)); System.out.println("uppercase:\t" + Character.isUpperCase(c)); System.out.println("lowercase:\t" + Character.isLowerCase(c)); System.out.println(d + " is:"); System.out.println("a letter:\t" + Character.isLetter(d)); System.out.println("a digit:\t" + Character.isDigit(d)); System.out.println("uppercase:\t" + Character.isUpperCase(d)); System.out.println("uppercase:\t" + Character.isLowerCase(d)); } } Output U is: a letter: true a digit: false uppercase: true lowercase: false 4 is: a letter: false a digit: true uppercase: false

Final QUESTIONS???