Programming Basics

	When it comes to being precise about an algorithm, a programming language is better than English

The Plan

	We will learn JavaScript over the next few lectures
			JavaScript is used with HTML in Web pages
			JavaScript is a contemporary programming language -- we will learn only its basics
			You will program in NotePad and run your program with your browser

Begin with HTML

	HTML is static … the contents of the file are displayed as given

JavaScript Needs HTML

	JavaScript must be surrounded by <script> tags in a Web page ...

Browsers Process JS

	When the browser comes to JavaScript, it processes it immediately

JS Can Build Pages

	JavaScript can add to a page using the document.write command ...

JavaScript is Cool

	JavaScript has many slick applications so it’s worth taking a couple of lectures to learn it
		We move on now to
		the basics, but first ...

Names In Programming

	In normal language, names, and the things they name -- their values -- usually cannot be separated
			In programming most names change values … a consequence of finite specification
			Titles (US_Open_Champ), Offices (Mayor), Roles (Juliet), etc. are familiar examples of names that change values
			Rules, Processes and Directions exploit the variable value: “Juliet moves to the window”

Variables

	Names in programming are identifiers
	The things they name are their values
	The package -- identifier & value -- is a variable, implying a possible change
			Identifiers have a specific structure in every programming language
			JS: letters, digits, _  start with letter, case sen.

Declarations

	To declare variables is to state what variables will be used
			Required … put declarations first in program
			Use the word:  var
			Follow with a list of variables separated by ,
			Terminate all statements with a semicolon  ;
			var x, input1, input2, rate;
			Give variables an initial value with  =
			var interestRate = 4, pi = 3.14159;

Values

	Programming languages allow several types of values: numeric, strings of letters, Boolean
			numbers:  1  0  -433  6.022e+23 .01
			not numbers:  1,000   106  5%   7±2
			strings:  "abc" 'efg' " "  "B&B's"  ""
			not strings:  '   '<tab>'  "a '  "\"
			Boolean:  true   false
			not Boolean:   T   F   yes   no

Assignment

	The universal form of assignment:
		<variable> <assignment symbol> <expression>
	For example ...
	day = hours/24;
			value of the variable on the left is changed to have the new value of expression on right
			read “=” as “is assigned” “becomes” “gets”
			right-to-left value flow

Expressions

	Expressions are like “formulas” saying how to manipulate existing values to compute new values, e.g. hours/24
			Operators:  +  -  *  /  %  produce numbers
			Operators: <  <=  ==  !=  >=  >   on numbers (or strings for == and !=) produce Booleans
			Operators:  &&   ||   !  on Booleans produce Booleans
			Grouping by parentheses is OK and smart
			seconds = ((days*24 + hours)*60 + min)*60

Overloading Plus

	The +  can be used to add numbers or join strings (concatenate)
			5 + 5  Û  10
			"a" + "b"  + "c" Û "abc"
			'5' + '5' Û  '55'
			The operand type determines the operation
			Combine a number and string???
			5 + '5' Û  '55’
			Rule: With an operand of each type, convert number to string, concatenate

First JS Program, Revisited

	Rewrite earlier code with new concepts

Conditional

	Conditionals test if an expression is true or not
			General form …
			if (<Boolean expression>)
			<Then statement>;
			For example
			if (day == "Friday")
			evening_plan = "party";

If-Then-Else

	Branch both ways with If-Then-Else
			if (<Boolean expression>)
			<Then statement>;
			else
			<Else Statement>;
			Example … if ((year%4)== 0) {
			leapYear = true;
			febDays = febDays+1;
			}
			else
			leapYear = false;

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