1. CS 18000 Problem Solving and Object Oriented Programming Spring 2019
Section LE2
Week 2: Lecture 4 January
Slides updated: 12:06pm January 16, 2019
Aditya Mathur
Professor, Department of Computer Science
Purdue University
West Lafayette, IN, USA
ps://

2. Review: Lecture 3 Primitive types Numbers
Two’s complement representation

3. Summary of primitive types (numbers)
Range
Sample
byte (8 bits)
-128:127
-3, 29, 127
short (16 bits)
-32,768: 32767
int (32 bits)
-2,147,483,648 :2,147,483,647
3, 29, 127
long (64 bits)
-263 :
float (32 bits)
1.40e-45 : 3.40e+38
-2.99, 4.56, 32.89E21
double (64 bits)
4.90e-324 : 1.79e+308
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4. Today Signed magnitude vs. two’s complement representation
Naming, constants, variables
Expressions
Assignments
The String class and strings
JOptionPane

5. Signed-magnitude vs 2’s complement representation
Consider 4-bits to represent numbers.
Signed magnitude representation (leftmost bit is the sign bit):
0111=7
1111=-7
2’s complement representation
0111=7
1111=-8
Range of numbers:
Signed magnitude: -7 to +7
2’s complement: -8 to +7
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6. Representing 0 0000=+0 1000=-0 Do we need two zeros? 1/14/2019
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7. Addition Signed magnitude 0111=+7 1111=-7 0111+1111=?110=?+6 or -6?
2’s complement
0111=+7
1001=-7
=0000
The student who asked this question deserves a big hand!!
Clap clap clap!
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8. Names Used to denote classes, objects, data
Contain characters; must start with a letter, or a $ sign or an underscore (_).
Examples: height, area1, Dog, $great, _init_
Length: unlimited, case sensitive.
Dog and dog are different names.
Convention: All class names begin with an uppercase letter; all other names begin with a lower case letter.
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9. Variables
A variable is something whose value may change during program execution.
Example: int gradesProcessed; denotes the number of students whose grades have been processed. Its value changes as each student’s grade is processed by a grade processing program.
Every variable has a name and a type.
Example: int hurricaneCategory; The name is hurricaneCategory and its type is int.
Every variable must be declared before it is used.
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10. Constants
A constant is something that cannot change during program execution.
Examples:
Integer constants: 0, 1, -1, +24, 29, , O14, 0x1B
Floating point constants: 0.0, e28,
Boolean constants: true, false
Character constants: ‘ ‘, ‘a’, ‘A’, ‘$’
String constants: “”, “ ”, “Hi!”, “Alice in Wonderland”
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11. Declarations int age; float height, area;
String name
boolean iAmAlive;
int x=1, y=0;
String firstName=“Harry”;
Why is “String” capitalized while other types are not?
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12. Named Constants
A constant can be named and the name used instead of the constant itself.
Examples:
final float pi= ;
final boolean dogsExist=true;
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13. [Simple] Expressions A mathematical formula to compute something.
a+b*c-d/e
avagadroNum*29/Math.E
(x-y%2)/(a+b)*(a+b)
Expressions are evaluated left to right.
Operator priority: * and / have higher priority than + and -.
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14. Simple expressions Expressions are used to compute “something”.
float x, y, z; // Declare x, y, z as variables of type float
x*y+z; // Arithmetic expression, results in float value
x<y; // Boolean expression, results in boolean value
String firstName=“Mary”, lastName= “Jones”;
firstName+ “ “ +lastName; // Results in a String
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15. Assignments A statement that assigns a value to a variable.
= denotes the assignment operator;
x=a+b*c-d/e; // Compute the value of the expression on the
right and assign to x
y=avagadroNum*29/Math.E;
z=(x-y%2)/((a+b)*(a+b));
++i and i++ // Both increment i by 1 but there is a difference; can you figure that out?
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16. More assignments float p=x*y+z; // p gets the value of x*y+z
boolean q=x<y; // q gets the value of x<y
String firstName=“Mary”, lastName= “Jones”;
String name= firstName+” “+lastName;
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17. Fun exercise Try the following: int p=1; int q=1; int r, z;
r=++p + ++p + ++p;
z=q++ + q++ + q++;
What are the values of r and z?
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18. Operations
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19. Operators: Arithmetic, relational, conditional
Arithmetic operators + - * / %
Relational operators ==
<
>
<=
>= !=
Boolean/conditional
operators ||
&& |
&
a+b*c-d
a/b
c%d
a==b
a<=b
a!=b
a==b||c<d
a<=b&&c>d
a!=b &&c>d||p+1<q
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20. Operators: bitwise Bitwise operators &: bitwise AND |: bitwise OR
^: bitwise exclusive OR
~: bitwise complement
Bitwise shift operators
<<: bitwise left shift
>>: bitwise right shift
>>>: unsigned right shift
a & b: logical and of a and b
a|b: logical OR of a and b
a <<3: shift bit pattern of a left by 3 bits
a>>2: shift bit pattern of a to the right by 2 bits
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21. Short circuit operations
int a=1, b=2, c=3, d=0; int p, q;
boolean x, y;
x=a>b && c>3;
y=a>b & c>3;
y=a>b & a>c/d;
p=a <<2: shift bit pattern of a left by 3 bits.
q=a>>2: shift bit pattern of a to the right by 2 bits
What should we get in each case?
float z=2.0; p=z>>2;
What should we get in this case?
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22. Division int x=0; System.out.println(3/x); // Will generate exception
System.out.println(3.0/x); // Generates Infinity
int x=0;
System.out.println(3.0%x); // Generates NaN
System.out.println(Math.sqrt(-2)); // Generates NaN
NaN: Not a number
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23. Strings
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24. Strings: basics A string is any sequence of Unicode characters
You may name a string as in the following:
String myDogsName;
myDogsName is an object of type String.
It can take any string as its value. For example,
“Max”, “Bently”, “Jake” and “Raja” are possible values of myDogsName.
What is the difference between 29 and “29”?
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25. Strings: assignment You may assign a value to a string object.
myDogsName=“Bently”; // Assuming that myDogsName has been declared
String myCarColor=“Red”;
All string objects must be declared before they are used.
Thus, it would be incorrect to assign a value to myDogsName before it has been declared.
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26. Strings: Other operations
You may apply a variety of operations to strings. Examples follow.
String commend=“Bently,”+ “ good girl!; // String catenation
String myCar=“It’s a Porsche”+ “, and I love it!” +”but maintenance is expensive.” // String catenation
String firstChar=commend.charAt(0); // Extract character at position 0
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27. Strings operations There exist a variety of operations on strings.
Statement
Operation used
String commend=“Bently,”+ “ good girl!”;
Catenation
char firstChar=commend.charAt(0);
Character extraction using charAt()
movieName.equals(“Fugitive”)
equals()
String.valueOf(29)
Convert int 29 to String “29”
During week 3 experiment with comparing two strings using
the == operator.
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28. Complex Numbers Not a primitive type
But you can define a class and do arithmetic on complex numbers.
For an example, visit:
Class Complex
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29. The edit, compile, execute cycle
.java file(s)
.class file(s)
Edit a
Java program
Compile your
program
Execute your
Syntax
error
Run time
Error or incorrect
output
No syntax
Correct
In CS 180 we shall use IntelliJ for editing, compiling and execution. IntelliJ is an Integrated Development Environment also known as an IDE.
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30. Illustration: Problem [Try yourself after the class]
Write a Java program that performs the following tasks:
Inputs
Radius r (meters) and height h (meters) of a circular tank.
level L of water in the tank in meters.
inflow rate f in m3/sec.
duration d for which water flows into the tank.
Computes the level L of water after d minutes.
Print, nicely formatted, L at time t=0 and L at time t=d.
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31. Another program (with GUI!)
import javax.swing.*; public class SimpleGUI { public static void main(String [] args){ String title="Got it!"; String question="Enter your password"; String social="Social Engineering"; String password=JOptionPane.showInputDialog(null, question, social, JOptionPane.QUESTION_MESSAGE); JOptionPane.showMessageDialog(null,password, title, JOptionPane.INFORMATION_MESSAGE); } }
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32. Did you learn “problem solving?”
“Problem solving” refers to a set of activities performed in order to solve a given problem. This is a generic term and applies to all disciplines, not only to Computer Science.
Sequence of steps for solving a problem as proposed by George Polya in the 1950’s :
Understand the problem
Devise a plan [Design]
Execute the plan [Code, Test etc]
Review solution
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33. Did you learn “what is OO programming?”
OO, or Object Oriented, programming refers to a set of activities that lead to a computer program, written in an object-oriented language, that when executed on a computer will solve a problem.
Java is an OO language used in CS 180.
Other OO languages include C++, C#, Delphi, Modula, Oberon, Objective C, Simula, Smalltalk, and many more!
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34. What is Problem solving and OO programming?
Understand the problem
Problem solving and OO programming refers to a set of activities that allow the mapping of a problem to a computer program, written in an object-oriented language, that when executed on a computer will solve the problem.
Design a solution [Algorithm]
Implement the algorithm
Test, debug, and correct the program
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35. Week 2: January 14-18, 2019 Hope you enjoyed this week!
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