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COMP 14 Introduction to Programming. Miguel A. Otaduy May 13, 2004. 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.

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Comp 14 introduction to programming

COMP 14Introduction to Programming

Miguel A. Otaduy

May 13, 2004


Review exercise
Review Exercise

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


Today in comp 14
Today in COMP 14

  • Java

    • special symbols

    • identifiers

    • data types

    • operators

    • expressions

    • Strings


Reading check up
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
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
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

  • 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


Special symbols
Special Symbols

+ - * /

. ; ? ,

<= != == >=


Word symbols aka reserved words or keywords

int

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
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
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 types what s a data type
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
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


Primitive data types numeric types
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
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 types characters
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 types booleans
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
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
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 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
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 precedence1
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
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
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
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
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


Questions evaluate these expressions
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
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
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
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 strings1
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
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


Summary1
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
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
Tomorrow

  • First QUIZ!

  • Writing a whole program


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