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COMP 14 Introduction to ProgrammingPowerPoint Presentation

COMP 14 Introduction to Programming

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Review Exercise

- Execution of c=2*a+b in a computer

Today in COMP 14

- Java
- special symbols
- identifiers
- data types
- operators
- expressions
- Strings

Reading Check-Up

syntax

- 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

False

floating-point

9

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

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!

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

float

double

char

void

public

static

throws

return

Word Symbolsaka reserved words, or keywords- 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

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

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

Primitive Data TypesWhat’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

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

- 4 represent integers

Primitive Data TypesNumeric 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

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 10308 with 15 significant digits

Max Value

127

32,767

2,147,483,647

> 9 x 1018

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

Primitive Data TypesCharacters

- 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'

newline character

(we'll discuss later)

Primitive Data TypesBooleans

- 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

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 %

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 / 3equals?

4

8 / 12equals?

0

14 % 3equals?

2

8 % 12equals?

8

Unary vs. Binary Operators

- Unary operators
- has only one operand
- example: - (negative, not subtraction)
-5

- Binary operators
- has two operands
- example: - (subtraction)
5 - 3

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)

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

Integral Expressions

- All operands are integers
- Result is an integer
- Examples:
2 + 3 * 5

3 + x – y / 7

x + 2 * (y – z) + 18

Floating-point Expressions

- All operands are floating-point numbers
- Result is a floating-point
- Examples:
12.8 * 17.5 – 34.50

x * 10.5 + y - 16.2

7.0 / 3.5

Mixed Expressions

- Operands of different types
- Examples:
2 + 3.5

6 / 4 + 3.9

- 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

2.0 + 3.5

1 + 3.9 1.0 + 3.9

Type Conversion (Casting)

- Used to avoid implicit type coercion
- Syntax
(dataTypeName) expression

- Expression evaluated first, then type converted to dataTypeName
- Examples:
(int) (7.9 + 6.7) = 14

(int) (7.9) + (int)(6.7) = 13

QuestionsEvaluate These Expressions

9 % 6

3

- (5 + 4) % 6
- (5 + 6) % 3.5
- (double) (13) / 2
- (double) (13 / 2)

11 % 3.5

not possible

13.0 / 2

6.5

(double) (6)

6.0

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"
- ""

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"?

0123456789...

11

(count the space)

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"

Parsing Numeric Strings

- String to int
Integer.parseInt(strExpression)

Integer.parseInt("6723") 6723

- String to float
Float.parseFloat(strExpression)

Float.parseFloat("345.76") 345.76

- String to double
Double.parseDouble(strExpression)

Double.parseDouble("1234.56") 1234.56

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

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) %

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)

Tomorrow

- First QUIZ!
- Writing a whole program

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