1. COMP 14 Introduction to Programming
Michele Weigle - COMP 14 - Spring 2004
COMP 14 Introduction to Programming
Miguel A. Otaduy
May 13, 2004

2. Michele Weigle - COMP 14 - Spring 2004
Review Exercise
Execution of c=2*a+b in a computer

3. Michele Weigle - COMP 14 - Spring 2004
Today in COMP 14
Java
special symbols
identifiers
data types
operators
expressions
Strings

4. Michele Weigle - COMP 14 - Spring 2004
Reading Check-Up
The rules of a language determine which instructions are valid.
True or False? Hello! is an example of a legal Java identifier.
If an operator has an integer and a floating-point operand, the result of the operation is a number.
The expression (int) (9.2) evaluates to
syntax
False
floating-point 9

5. Michele Weigle - COMP 14 - Spring 2004
Introduction
Computer program: a sequence of statements whose objective is to accomplish a task
Programming: process of planning and creating a program
Programming language: a set of rules, symbols, and special words

6. Michele Weigle - COMP 14 - Spring 2004
Sample Java Program
public class Hello {
public static void main (String[] args)
System.out.println ("Hi There!"); }
Upon execution, this program would display
Hi There!

7. Programming Languages
Michele Weigle - COMP 14 - Spring 2004
Programming Languages
Programming languages have rules of grammar just as English does
syntax rules - which statements are legal and which are not
semantic rules - determine the meaning of the instructions
token - smallest individual unit of a program
special symbols
word symbols
identifiers

8. Michele Weigle - COMP 14 - Spring 2004
Special Symbols
+ - * /
. ; ? ,
<= != == >=
the 3rd row contains two characters that together (with no space between them) are considered to be a single symbol

9. Word Symbols aka reserved words, or keywords
Michele Weigle - COMP 14 - Spring 2004
Word Symbols aka reserved words, or keywords
int
float
double
char
void
public
static
throws
return
reserved words are always all lowercase
each word symbol is considered to be a single symbol
cannot be used for anything other than their intended
purpose in a program
shown in blue typewriter font in textbook
full table in Appendix A

10. Michele Weigle - COMP 14 - Spring 2004
Identifiers
Names of things (variables, constants, methods) in your programs
Can be composed of any combination of letters, digits, underscore (_), and dollar sign ($)
Cannot begin with a digit
May be any length
Java is case-sensitive
Total, total, and TOTAL are different identifiers

11. Michele Weigle - COMP 14 - Spring 2004
Illegal Identifiers

12. Michele Weigle - COMP 14 - Spring 2004
Questions
Classify the following as legal or illegal identifiers:
My First Program
my1stProgram
1stProgram
$money
an_identifier
Jane'sProgram
illegal
legal
illegal
legal
legal
illegal

13. Primitive Data Types What’s A Data Type?
Michele Weigle - COMP 14 - Spring 2004
Primitive Data Types What’s A Data Type?
A set of values and the operations that can be performed on those values
Primitive data are fundamental values such as numbers and characters
Operations are performed on primitive types using built-in operators
certain types of operations can only be performed on certain types of data
example: you can multiply numbers, but not words

14. Michele Weigle - COMP 14 - Spring 2004
Primitive Data Types
8 primitive data types in Java
4 represent integers
byte, short, int, long
2 represent floating point numbers
float, double
1 represents characters
char
1 represents boolean values
boolean

15. Primitive Data Types Numeric Types
Michele Weigle - COMP 14 - Spring 2004
Primitive Data Types Numeric Types
The difference between the various numeric primitive types is their size, and therefore the values they can store:
Type
byte
short
int
long
float
double
Storage
8 bits
16 bits
32 bits
64 bits
Min Value
-128
-32,768
-2,147,483,648
< -9 x 1018
+/- 3.4 x 1038 with 7 significant digits
+/- 1.7 x with 15 significant digits
Max Value
127
32,767
2,147,483,647
> 9 x 1018
float - at most 6 or 7 places after the decimal point
double - at most 15 places after the decimal point
some compilers will complain if you use float, so we will use double throughout this class

16. Michele Weigle - COMP 14 - Spring 2004
Integers
Examples: -6728, -67, 0, 78, 36782
Positive integers do not have a '+' sign in front of them (but they can)
No commas are used in an integer
commas in Java are used to separate items in a list

17. Primitive Data Types Characters
Michele Weigle - COMP 14 - Spring 2004
Primitive Data Types Characters
A char stores a single character from the Unicode character set
an ordered list of characters, and each character corresponds to a unique number
uses 16 bits per character, allowing for 65,536 unique characters
Character literals are delimited by single quotes:
'a' 'X' '7' ' ' '$' ',' '\n'
ordered list of characters
for example, the value 65 represents uppercase 'A'
66 represents uppercase 'B'
the full list of Unicode / ASCII is in Appendix C of the textbook
newline character
(we'll discuss later)

18. Primitive Data Types Booleans
Michele Weigle - COMP 14 - Spring 2004
Primitive Data Types Booleans
Only two valid values
true or false
uses 1 bit for storage
Represent any situation that has 2 states
on - off
true - false
true and false are reserved words
We'll see a lot more of booleans and boolean expressions later on in the semester

19. Arithmetic Expressions
Michele Weigle - COMP 14 - Spring 2004
Arithmetic Expressions
Expression - a combination of one or more operands and their operators
Arithmetic expressions compute numeric results and make use of the arithmetic operators:
If either or both operands associated with an arithmetic operator are floating point, the result is a floating point
Addition +
Subtraction -
Multiplication *
Division /
Remainder %

20. Division and Remainder
Michele Weigle - COMP 14 - Spring 2004
Division and Remainder
If both operands to the division operator (/) are integers, the result is an integer (the fractional part is discarded)
The remainder, or modulus, operator (%) returns the remainder after dividing the second operand into the first (only works with integer types)
14 / equals? 4
8 / equals?
14 % equals? 2
8 % equals? 8

21. Unary vs. Binary Operators
Michele Weigle - COMP 14 - Spring 2004
Unary vs. Binary Operators
Unary operators
has only one operand
example: - (negative, not subtraction) -5
Binary operators
has two operands
example: - (subtraction)
5 - 3

22. Michele Weigle - COMP 14 - Spring 2004
Operator Precedence
Determines the order in which operators are evaluated:
multiplication, division, and remainder
addition, subtraction, and string concatenation
arithmetic operators with the same precedence are evaluated from left to right
Parentheses can be used to force the evaluation order (just like in math)

23. Michele Weigle - COMP 14 - Spring 2004
Operator Precedence
What is the order of evaluation in the following expressions?
a + b + c + d + e
a + b * c - d / e 1 2 3 4 3 1 4 2
a / (b + c) - d % e 2 1 4 3
a / (b * (c + (d - e))) 4 3 2 1

24. Michele Weigle - COMP 14 - Spring 2004
Integral Expressions
All operands are integers
Result is an integer
Examples:
2 + 3 * 5
3 + x – y / 7
x + 2 * (y – z) + 18
in these expressions, x, y, and z are some unknown numbers.

25. Floating-point Expressions
Michele Weigle - COMP 14 - Spring 2004
Floating-point Expressions
All operands are floating-point numbers
Result is a floating-point
Examples:
12.8 * 17.5 – 34.50
x * y
7.0 / 3.5
in these expressions, x and y are some unknown numbers.

26. Michele Weigle - COMP 14 - Spring 2004
Mixed Expressions
Operands of different types
Examples:
6 /
Integer operands yield an integer result
Floating-point operands yield a floating-point result
If both types of operands are present, the result is a floating-point number
implicit type coercion
Precedence rules are followed
if you have both integer and floating -point operands, the integer will be converted to a floating-point number and the operation will take place -- the result will be floating-point

27. Type Conversion (Casting)
Michele Weigle - COMP 14 - Spring 2004
Type Conversion (Casting)
Used to avoid implicit type coercion
Syntax
(dataTypeName) expression
Expression evaluated first, then type converted to dataTypeName
Examples:
(int) ( ) = 14
(int) (7.9) + (int)(6.7) = 13
casting a floating-point number to an integer truncates everything after the decimal point
(int) 14.6
7 + 6
the textbook has very nice examples of mixed expressions and casting on pgs make sure you take a look at them and understand the answers

28. Questions Evaluate These Expressions
Michele Weigle - COMP 14 - Spring 2004
Questions Evaluate These Expressions
(5 + 4) % 6
(5 + 6) % 3.5
(double) (13) / 2
(double) (13 / 2)
9 % 6 3
11 % 3.5
not possible
13.0 / 2
6.5
(double) (6)
6.0

29. Michele Weigle - COMP 14 - Spring 2004
The class String
String
sequence of zero or more characters
enclosed in double quotation marks
null or empty strings have no characters
numeric strings consist of integers or decimal numbers
length is the number of characters in a string
The class String is used to manipulate strings
Examples:
"Hello World"
"1234"
"45.67"
""
note the null, or empty, string

30. Michele Weigle - COMP 14 - Spring 2004
Strings
Every character has a position in the string (starting with 0)
"Hello World"
The length of the string is the number of characters in it
what's the length of "Hello World"? 11
(count the space)

31. Parsing Numeric Strings
Michele Weigle - COMP 14 - Spring 2004
Parsing Numeric Strings
In Java, input from the user comes in the form of a string
we need to know how to get the number values out of the string
Numeric String
a string with only integers or decimal numbers
"6723", "-823", "345.76"

32. Parsing Numeric Strings
Michele Weigle - COMP 14 - Spring 2004
Parsing Numeric Strings
String to int
Integer.parseInt(strExpression)
Integer.parseInt("6723") 6723
String to float
Float.parseFloat(strExpression)
Float.parseFloat("345.76")
String to double
Double.parseDouble(strExpression)
Double.parseDouble(" ")
the capital letters in Integer, Float, and Double are important -- Java is case-sensitive!

33. Michele Weigle - COMP 14 - Spring 2004
Summary
Identifiers
can be composed of any combination of letters, digits, underscore (_), and dollar sign ($)
cannot begin with a digit
Java is case-sensitive
Data Types
main integer type: int
main floating-point type: double
others: char, boolean

34. Michele Weigle - COMP 14 - Spring 2004
Summary
Arithmetic Operators:
If one of the operands is floating-point, the result is a floating-point
Can only use % with two integer operands
Casting
(int) (54.9) - truncates the floating-point number
(double) (23) - adds a .0 to the integer
addition +
subtraction -
multiplication *
division /
remainder (mod) %

35. Michele Weigle - COMP 14 - Spring 2004
To do
Homework 1 due tonight
Homework 2 due tomorrow night
Algorithm design
Theory questions
First program (after tomorrow’s class)
Read ch. 2 (pp. 37-end)

36. Michele Weigle - COMP 14 - Spring 2004
Tomorrow
First QUIZ!
Writing a whole program