Concepts of Algorithmic Thinking Get With the Program: Basic Programming Concepts

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Concepts of Algorithmic Thinking Get With the
ProgramBasic Programming Concepts

• D.A. Clements

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Just a thought

• JavaScript is
• The earliest known writing by Java Man.
• Programming language for Web pages.
• Instructions in the Starbucks bag on how to brew
  good coffee.

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Programs vs. algorithms
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Five Essential Properties of Algorithms

• Input specified
• Output specified
• Definiteness
• Effectiveness
• Finiteness

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Program vs. Algorithm

• A program is an algorithm that has been
  customized to
• solve a specific task
• under a specific set of circumstances
• using a specific language
• Algorithm is general
• Program is specific

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Overview

• Basic programming concepts

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Programming Concepts

• Programming Act of formulating an algorithm or
  program
• Basic concepts have been developed over last 50
  years to simplify common programming tasks
• Concepts will be expressed in JavaScript in this
  course
• Easy syntax
• Immediate results

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Overview

• Names, values, variables
• Variable declarations
• Data types
• Assigning values to variables
• Expressionscalculating values
• Conditionals, branches, or tests
• Loops or iterations

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An Algorithm
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An Algorithm
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Names, values, and variables

• Whats in a name?

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Names, Values, and Variables

• Names Have Changing Values
• U.S. President
• current value of George W. Bush
• previous values of Bill Clinton, George
  Washington
• Names in a Program Are Called Variables
• Variables store values and give you a handy way
  to refer to the current value in the variable
• Like we say The President to refer to our
  current president

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Identifiers and Their Rules

• Identifier the name of a variable
• A variable name refers to the present value of
  the variable, just like The President refers to
  the current president.
• Case sensitive
• HOME ? Home ? home

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Identifiers and Their Rules
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Variable Declarations

• Example var home

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A Variable Declaration Statement

• Declaration State what variables will be used
• Command is the word var
• For example, a program to calculate area of
  circle given radius, needs variables area and
  radius
• var radius, area
• The declaration is a type of statement
• The declaration allocates space in memory to the
  variable
• Declare your variables at the top so you can find
  them easily

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The Statement Terminator

• A program is a list of statements
• The statements may be run together on a line
• Use white space to help you
• read your code
• understand your program
• End each statement withthe statement terminator
  symbol
• In JavaScript, all statements terminate with the
  semicolon ( )

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Names, Values, And Variables

• Declaring a variable
• Names a particular area in computer memory where
  you can store values
• Gives you a name, or handle, that is independent
  of the current value

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Rules for Declaring Variables

• Every variable used in a program must be declared
  (before it is used)
• In JavaScript declaration can be anywhere in the
  program
• Programmers prefer to place them first
• Undefined values
• Variable has been declared but does not yet have
  a value
• var number1 // undefined value
• var number2 42 // initialized to the value 42

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Initializing a Declaration

• We can set an initial value as part of
  declaration statement
• var taxRate .088
• Related variables may be grouped in one
  declaration/initialization unrelated variables
  are usually placed in separate statements
• var num1 42, num2, num3 var num1
  42 var num2 var num3

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Data types

• Currency, string, number, boolean, date/time

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Three Basic Date Types of Javascript

• Numbers
• Strings
• Booleans
• These kind of values are called data types or
  just types

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Numbers

• Rules for Writing Numbers
• No "units" or commas
• Up to 10 significant digits
• Range from 10-324 to 10308

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Strings

• sequences of keyboard characters
• always surrounded by single ( ' ' ) or double
  quotes ( " " )
• No smart quotes!
• initialize a declaration
• var hairColor "black"
• quotes can nest
• firstLine Johnson called, Dude!

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Strings

• Rules for Writing Strings
• Must be surrounded by single or double quotes
• Allow most characters except return (Enter),
  backspace, tab, backslash (\)
• Double-quoted strings can contain single quoted
  strings and vice versa
• The apostrophe ( ' ) is the same as the single
  quote
• Any number of characters allowed in a string
• Minimum number of characters is zero ( "" ),
  which is the empty string

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Literals

• String Literals stored in the computer
• Quotes are removed (they are only used to delimit
  the string literal)
• Any character can be stored in memory
• Even a character that cannot be typed can be
  stored, using escape mechanism
• in JavaScript, the backslash ( \ )

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Boolean Values

• Two logical values True and False
• They are values, not identifiers or strings
• Used implicitly throughout programming process
  only occasionally for initializing variables
• Mostly used to compare data or make decisions

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Comments

• //Single-line JavaScript comment
• /Multi-line JavaScript comment continues for
  more than one line/
• Comments allow you to
• Annotate your code
• Remind yourself what you did and why
• Notes for yourselfor someone elsesix months
  from now when youre making an update!

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Assigning values to variables

• All about assignment statements

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Assigning Values to Variables

• Assign values to variables with an assignment
  operator.
• We'll use for now.
• var yourAge, acctBal, custName
• yourAge 32 //store 32 in yourAge
• acctBal 100.75 //store 100.75 in acctBal
• custName 'Jeff' //store 'Jeff" in custName
• isCustomer true //store boolean true in
  isCustomer (no quotes)
• Var yourName 'Jeff' //alternate all-in-one line
  assignment statement

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Assignment Statement

• ltVariablegt ltassignmentgtltexpressiongt
• Flow moves from right to left.
• Results of the ltexpressiongt replace the value
  stored in the ltvariablegt.

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Assigning Values to Variables and Variables to
Variables

• We can also assign one variable to another

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Other Assignment Operators
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Assignment

• Three Key Points
• All three of the components must be given
• if anything is missing, the statement is
  meaningless
• Flow of value to identifier is always right to
  left
• Values of any variables used in the expression
  are always their values before the start of the
  execution of the assignment

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Expressions

• Calculating values in variables

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An Expression and its Syntax

• Algebra-like formula called an expression
• Describe the means of performing the actual
  computation
• Built out of values and operators
• Standard arithmetic operators are symbols of
  basic arithmetic

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Arithmetic Operators

• Multiplication must be given explicitly with the
  asterisk ( ) multiply operator
• Multiply and divide are performed before add and
  subtract
• Unless grouped by parentheses
• Within parentheses multiply and divide are
  performed first
• JavaScript does not have an operator for exponents

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Relational Operators

• Make comparisons between numeric values
• Used in if statements and stop tests in loops
• Outcome is a Boolean value, true or false
• lt less than
• lt less than or equal to
• equal to
• ! not equal to
• gt greater than or equal to
• gt greater than

Note Difference between and compares
values assigns a value to a variable
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Logical Operators

• To test two or more relationships at once
• Teenagers are older than 12 and younger than 20
• Logical AND
• Operator is
• Outcome of a b is true if both a and b are
  true otherwise it is false
• Logical OR
• Operator is
• Outcome of a b is true if either a is true or
  b is true
• Logical NOT
• Operator is !
• Unary operator. Outcome is opposite of value of
  operand

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Operators (cont'd)

• Addition
• Adds numbers
• 4 5 produces 9
• Concatenation
• Strings text together
• "four" "five" produces "fourfive
• "four" 5" produces "four5"

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Conditionals, branches, or tests

• Adding logic to an algorithm

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Conditional Statement Syntax

• if ( ltBoolean expressiongt )
• ltthen-statementgt
• Boolean expression is a relational expression
  then-statement is any JavaScript statement

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If Statements Control Flow

• The Boolean statement, called a predicate, is
  evaluated, producing a true or false outcome
• If the outcome is true, the then-statement is
  performed
• If the outcome is false, the then-statement is
  skipped
• Then-statement can be written on the same line as
  the Boolean or on the next line

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Compound Statements

• Sometimes we need to perform more than one
  statement on a true outcome of the predicate test
• You can have a sequence of statements in the then
  clause
• Group these statements using curly braces
• They are collected as a compound statement

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if/else Statements

• To execute statements if a condition is false
• if ( ltBoolean expressiongt )
• ltthen-statementsgt
• else
• ltelse-statementsgt
• The Boolean expression is evaluated first
• If the outcome is true, the then-statements are
  executed and the else-statements are skipped
• If the outcome is false, the then-statements are
  skipped and the else-statements are executed

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Nested if else Statements

• The then-statement and the else-statement can
  contain an if/else
• The else is associated with the immediately
  preceding if
• Correct use of curly braces ensures that the else
  matches with its if

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Nested if/else Statements
if (ltBoolean exp1gt) if (lt Boolean exp2gt)
ltthen-stmts for exp2gt
else ltelse-stmts for exp1gt
if (ltBoolean exp1gt) if (lt Boolean exp2gt)
ltthen-stmts for exp2gt else
ltelse-stmts for exp2gt
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The Espresso Program
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The Espresso Program

• Line 3 is a basic conditional statement
• Lines 4-4c use an if statement with conditionals
  in the then statement
• Line 5 uses basic if statement
• Lines 6, 7 compute using arithmetic operators

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In future lectures
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Coming soon to a computer near you

• Loops, or iterations, repeat code as many times
  as necessary
• The number of loops can be scripted
• Arrays are lists or collections
• Loops make it easy to iterate through all the
  elements in an array
• Functions allow you to package an algorithm for
  use in multiple places

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Summary

• Programming is the exact specification of an
  algorithm
• JavaScript is typical with many rules
• Learning strategy
• Do the reading first
• Practicing is better than memorizing for learning
  the rules
• Use the program-save-reload-check plan
• Precision is your best friend

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End papers

• Why is programming fun?
• First is the sheer joy of making things. As the
  child delights in his mud pie, so the adult
  enjoys building things, especially things of his
  own design. I think this delight must be an image
  of God's delight in making things, a delight
  shown in the distinctness and newness of each
  leaf and each snowflake.
• Source Frederick P. Brooks, Jr. The Mythical
  Man-Month Essays on Software Engineering.