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

2. 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

3. QUESTIONS???

4. Basic Operations Recap

5. 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;

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

7. Basic Operations w/Integers Code Example 1
public class IntegerOperations {
public static void main(String[] args) {
int a;
int b;
a = ; // 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

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

9. 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 =
b =
c =
d = 1.0
Question
Variable d is a double or an integer?

10. 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.

11. 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

12. 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

13. 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
Note
Math.round(y);
(int) (y + 0.5);
These are the same.

14. 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

15. 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); }

16. 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 ‘\\’

17. 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

18. 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

19. 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;

20. 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)

21. 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

22. 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 !

23. 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

24. 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;

25. 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);

26. 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’);

27. 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

28. 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

29. Final QUESTIONS???