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Put the hardcopy of Project 1b in the box |
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Please keep up on reading ... |
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When it comes to being precise about an
algorithm, a programming language is better than English |
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We will learn JavaScript over the next few
lectures |
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JavaScript is used with HTML for Web pages |
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JavaScript is a contemporary programming
language -- we will learn only its basics |
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You will program in NotePad and run your program
with your browser |
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JavaScript must be surrounded by <script>
tags … build a test page |
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Write and run a program to figure 2+2 |
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In normal language, names, and the things they
name -- their values -- usually cannot be separated |
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In programming most names change values … a
consequence of finite specification |
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Titles (US_Open_Champ), Offices (Mayor), Roles
(Juliet), etc. are familiar examples of names that change values |
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Rules, Processes and Directions exploit the
variable value: “Juliet moves to the window” |
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Names in programming are identifiers |
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The things they name are their values |
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The package -- identifier & value -- is a variable,
implying a possible change |
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Identifiers have a specific structure in every
programming language |
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JS: letters, digits, _ start with letter, case sen. |
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To declare variables is to state what variables
will be used |
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Required … put declarations first in program |
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Use the word:
var |
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Follow with a list of variables separated by , |
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Terminate all statements with a semicolon ; |
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var x, input1, input2, rate; |
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Give
variables an initial value with = |
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var interestRate = 4, pi = 3.14159; |
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Programming languages allow several types of
values: numeric, strings of letters, Boolean |
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numbers:
1 0 -433
6.022e+23 .01 |
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not numbers:
1,000 106 5%
7±2 |
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strings:
"abc" 'efg' " "
"B&B's"
"" |
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not strings:
' '<tab>' "a ' "\" |
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Boolean:
true false |
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not Boolean:
T F yes
no |
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The universal form of assignment: |
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<variable> <assignment symbol>
<expression> |
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For example ... |
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day = hours/24; |
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value of the variable on the left is changed to
have the new value of expression on right |
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read “=” as “is assigned” “becomes” “gets” |
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right-to-left value flow |
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Expressions are like “formulas” saying how to
manipulate existing values to compute new values, e.g. hours/24 |
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Operators:
+ - *
/ % produce numbers |
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Operators: <
<= == !=
>= > on numbers (or strings for == and !=)
produce Booleans |
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Operators:
&& || !
on Booleans produce Booleans |
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Grouping by parentheses is OK and smart |
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seconds = ((days*24 + hours)*60 + min)*60 |
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The +
can be used to add numbers or join strings (concatenate) |
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5 + 5 Û 10 |
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"a" + "b" + "c" Û
"abc" |
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'5' + '5' Û '55' |
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The operand type determines the operation |
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Combine a number and string??? |
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5 + '5' Û '55’ |
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Rule: With an operand of each type, convert
number to string, concatenate |
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Write and run a program to figure 2+2 |
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Conditionals test if an expression is true or
not |
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General form … |
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if (<Boolean expression>) |
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<Then statement>; |
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For example |
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if (day == "Friday") |
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evening_plan = "party"; |
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Branch both ways with If-Then-Else |
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if (<Boolean expression>) |
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<Then statement>; |
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else |
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<Else Statement>; |
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Example … if ((year%4)== 0) { |
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leapYear = true; |
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febDays = febDays+1; |
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} |
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else |
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leapYear = false; |
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Programming is the exact specification of an
algorithm |
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JavaScript is typical … with many rules |
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Learning strategy |
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Do the reading first |
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Practicing is better than memorizing for
learning the rules |
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Use the program-save-reload-check plan |
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Precision is your best friend |
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Notes
