Announcements

	Put the hardcopy of Project 1b in the box
		Please keep up on reading ...

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 for 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

Using JavaScript in HTML

	JavaScript must be surrounded by <script> tags … build a test page

First JS Program

	Write and run a program to figure 2+2

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

	Write and run a program to figure 2+2

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