The document provides an introduction to programming concepts such as variables, data types, basic math operations, and order of operations. It explains how variables store and represent data in computer memory and how their values can be manipulated using assignment statements and basic math. The document also introduces potential issues around data type conversion and order of operations that programmers need to be aware of.

1. Introduction to Programming
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2. Where are we?
• Web Technology Stack
• 10 Minute Digression on Servers
– Client/server model
– Server Architecture
– Server Software Background
• The physical vs. logical
– Where do my files live?
– Where are they processed?
• Introduction to Programming
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3. Web Technology Stack
Data – What does it know?
Behavior – What does it do?
Behavior – What does it do?
Presentation – What does it look like?
Structure – What does this logically mean?
Richness
of the
Experience

4. Basic Server Architecture
HTTP request
` HTTP response
Web Browser Web Server Database Server
A server is a computer
PHP
This is the model! Script optimized to share
resources, such as files,
printers, web sites,
What is our physical databases, and email,
architecture? over a network.

5. About Apache
• The Apache http server project is an
effort to develop and maintain an open
source http server for modern operating
systems (Linux, MS, OSX, …). The goal is
to provide a secure, efficient, and
extensible server that meets all standards
• http://httpd.apache.org
• Maintained by the Apache foundation

6. Stats of Web Server types
http://www.greatstatistics.com/serverstats.php

7. What the Busiest 1M Websites use
Totals for Active Servers Across All Domains - May 2010
nginx lighttpd
9% 0%
Google
13%
Apache
Microsoft 59%
19%

8. About PHP
• PHP stood for Personal Home Page (like a shell script)
• PHP now stands for PHP: Hypertext Preprocessor
(yes, it’s a recursive definition)
• PHP is HTML-centric and lives inside/along side HTML
• PHP is used to generate dynamic web pages
• PHP runs on the web server
– When the user requests a dynamic web page (typically a
.php file), the web server calls the PHP interpreter to
read the requested file
– The PHP interpreter parses the PHP commands (code) and
typically generates an .html file, which is returned to the
user
– PHP can use data passed to it from the web page and
access data in a database server

9. About MySQL
• MySQL is an open source database server
that is available for all/most operating
systems
– SQL: Structured Query Language
• Introduced in 1995 with version 3.23
• Now, version 5.X
• How open source is MySQL?
– MySQL is owned by MySQL AB, a for profit firm
– In 2008, Sun Microsystems acquires MySQL AB
– In 2009, Oracle Corporation acquires Sun
Microsystems

10. Apache, PHP & MySQL
• These open source products are easily installed
by developers and used commercially
• Your OS, Apache, MySQL, PHP – [X A M P]!
– LAMP, WAMP, and MAMP
• LAMP stacks are widely used to serve many content
applications
– Webmail, Blogs, Wikis, CMSs, etc.
• Great for Virtual Hosting!
– It is the server stack you get for $5/month from
HostGator, GoDaddy, etc.

11. Introduction to Programming
• Slides are from a course teaching “young
people” to program
– Apologize if too elementary
– Apologize if too advanced
• There will be some opportunities to program
– All examples are online and expectation is that
you will run the examples and review them here
and for homework
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12. What are the Attributes of Good Programmers?
• Humility
• Love of Learning
• Detail-orientedness
• Adaptability
• Passion
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13. What is programming?
• Very simply, programming means telling a
computer to do something
– Computers are dumb machines
• A computer program is made up of a number of
instructions
– An instruction is a basic command given to a
computer, usually to do a single, specific thing
• Software is a program or a collection of programs
that run on your computer
– Sometimes the software runs on another computer
that yours is connected to, like a web server.
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14. Programming Languages
• Inside, all computers use a
binary (0/1) language
– Humans don’t speak binary
very well
• A programming language
lets humans write in ways
we “understand”
– It is then translated into
binary for the computer to
use
• There are lots of
programming languages
– HTML, CSS, Javascript, PHP,
Perl, Python, Basic, C, C++,
Java, etc.
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15. Vocabulary
• Instructions
– echo “Hello there!”;
• Keywords
– A keyword is a special word that is part of a programming language (also
called a reserved word).
• Coding/Editing
– Writing a number of instructions that will perform a specific set of functions
• Compiling
– Converting the “human readable” instructions into the binary language that
the computer understands
• Executing
– A fancy way of saying “running your program”
• Interpreting
– Sometimes, converting to binary and executiing takes place instruction by
instruction, this is interpreting
• Debugging
– The process of finding errors (bugs) and correcting them
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16. What could go wrong?
• Syntax bugs – Errors prior to execution (perhaps in your editor)
– Syntax is the spelling and grammar rules for a programming language, a
syntax error means that something is typed that just won’t work
• Runtime bugs - Errors during execution
– Runtime errors usually crash or stop the execution of your program with
some clues, called a Traceback - like what file, line number, or even error
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17. *Class caveats & kludges*
• All programming examples are on my server:
– http://jamesmarcus.net/bwa/introprog
• We will use our browsers as an output device to
print simple results – our test jig!
– We are not printing (real) web pages (yet)
– We do not have the ability to get input values (yet)
• The example PHP code is embedded in a
comment tag and can be viewed using “View
Source”
– Examples must be changed to run on your web server
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18. The programming cycle
• Edit • Edit and Save
– Write code <1hello1.php>
• Execute • Execute <1hello1.php>
– Run a program – Browser:
– Get a webpage http://localhost/bwa/int
roprog/1hello1.php
• Test & Debug
– “Inspect what you
• Test & Debug the
expect” results
– If you find a bug, back – Review results for a
to editing! variety of inputs
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19. Our first PHP program
• XAMPP Control – start web server!
• Create in /htdocs/bwa/introprog the file
<1hello1.php>
<?php
print “Hello”;
print “ and Hello to you.”;
?>
• Start and end of a PHP code block
• A PHP code block
• PHP instructions end with a ‘;’
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20. Analyzing our first PHP program
• File naming convention
– Files that contain PHP code have a .php extension
• PHP code blocks start and end with:
– <?php and ?>
– PHP instructions end with a ‘;’
• PHP has two simple output statements:
– print
– echo
• Using the browser as a text output device
– Yet, it is still a browser
• We can add simple text formatting. How?
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21. Playing with our first PHP program
• Add simple text/HTML formatting to
<1hello1.php> to create <1hello2.php>
• Introduce errors to <1hello2.php>
– Syntax errors: Where/when do syntax errors occur?
– Runtime errors: Where/when do runtime errors
occur?
• Multiple code blocks: <1hello3.php>
– What is going on in between the code blocks?:
<1hello4.php>
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22. Memory & Variables - Remember Me!
• Most all ‘useful’ programs:
– Get input
– Process the input
– Produce output
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23. Feed Me, Seymour
• The computer needs input
– But in order to do something with the input, the
computer has to remember it or keep it somewhere
– The computer keeps things, including input (and the
program itself), in its memory
• Computer memory - a bunch of on/off switches
– You can write to the memory (set the switches)
– You can read from the memory (look at how the
switches are set, without changing them)
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24. Naming Memory
>> Teacher = “Mr. Morton” • What happened?
>> print Teacher – We created a thing that
is made up of (a string
of) characters and gave it
• What do you expect a name, Teacher
from this “pseudo- • The equal sign ‘=‘ says
code” code snippet? to assign or “make
equal to”
– You assigned the name
Mr. Morton Teacher to the string of
letters “Mr. Morton”
<2teacher1.php>
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25. But wait…
• It’s just like if someone
said, “Write down your
address.”
– What would you write?
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26. Variables
• Programmers do not have to
think about how and where
memory stores things (like the
string of letters)
– We assign a value to a name and
then retrieve the value later
• The name assigned to the
value, like Teacher, is called a
variable
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27. Types of Variables
• Variables exist for
– Strings (series of characters)
– Numbers (integers, reals)
– And other interesting stuff
• Boolean: true/false
• Groups of groups of letters or numbers – arrays!
• Explicit variable declaration
• Implicit variable declaration
• And in between
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28. Using Variables
print 5 + 3;
$First = 5;
<3variables1.php>
$Second = 3;
print $First + $Second;
$Third = $First + $Second;
print $Third;
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29. What’s her name?
$MyTeacher = “Mrs. Goodyear”;
$YourTeacher = $MyTeacher;
print $MyTeacher;
Mrs. Goodyear
print $YourTeacher;
Mrs. Goodyear
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30. What if…
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31. What’s in a name?
• In most modern programming languages, you can call a
variable anything you want (well, almost):
• It can be as long as you want
• It can have letters and numbers in it, as well as special
characters, like the underscore character (_)
• It usually is case-sensitive (uppercase and lowercase
matter)
– Are teacher and TEACHER two different names?
• It cannot have spaces
• It may require a special starting character
• In PHP, variables start with $, i.e., $Teacher
• In other languages, read the documentation
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32. String Variables
• A character, or series of characters (letters,
numbers, or punctuation), is called a string
– The way you state that you are making a string is
to put quotes around the characters
– PHP and other languages are not too fussy about
whether you use single or double quotes
$teacher = “Mr. Morton”;
$teacher = „Mr. Morton‟;
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33. Numbers as Strings
Strings as Numbers
$first = 5;
$second = 3;
print $first + $second; <4concat1.php>
$first = „5‟;
$second = „3‟;
print $first + $second;
• Huh? Adding two strings?
– Is that what we mean to do?
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34. Fancy word time: concatenate
• It’s not really correct to say we want to “add”
strings. (Though PHP lets us do so.)
• When you put characters or strings together
to make a longer string, we call it
concatenation.
• In PHP, two strings are concatenated by the
dot ‘.’ operator:
<4concat2.php>
$newstring = $string1 . $string2;
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35. How variable is a variable?
• Variables are called “variables” for a reason
– It’s because they are . . . well . . . variable!
– The value assigned to them can vary or change
– Remember the MyTeacher example
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36. How variable is variable?
$teacher = “Mr. Morton”;
$teacher = “Mr. Smith”;
$print teacher;
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37. The new me!
• You can make a variable equal to itself:
$Score = 7;
$Score = $Score;
• Big woop! It is just the same old me.
$Score = $Score + 1;
print $Score;
• Woop, woop! It is a whole new me!
<5increment1.php>
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38. Incrementing a variable
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39. Variable Wrap-up!
• A variable can be reassigned (the tag can be stuck
on a new thing) at any time by a program
– One of the most common “bugs” in programming is
changing the wrong variable or changing the right
variable at the wrong time
– One way to prevent this is to use variable names that
are easy to remember and have contextual meaning
• $t = 'Mr. Morton' or $x1796vc47blahblah = 'Mr. Morton'
work but have no meaning
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40. Quiz
• Once you have created a variable, can you change
the value assigned to it?
• With variable names, is $TEACHER the same as
$TEACHEr?
• Is ‘Blah’ the same as “Blah”?
• Is ‘4’ the same as 4?
• Is “10” a number or a string?
• How do you tell PHP that a variable is string or a
number?
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41. Basic Math
• The four basic operations:
– Addition: +
– Subtraction: -
– Multiplication: *
– Division: /
• Exponentiation [PHP: pow($base, $exponent)]
– Raising a number to a power: 25= 2*2*2*2*2
• Modulus [PHP: %]
– Clock arithmetic
• Increment and decrement
$Score = $Score + 1;
++$Score;
$Score += 1;
• Really big numbers, really small numbers
– Overflow, underflow, e-notation
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42. Order of Operation
• PEMDAS
– Parentheses
– Exponents
– Multiply
– Divide
– Add
– Subtract
• But be kind and use parentheses!
– (2 + 3) * 4 = 20
– 2 + (3 * 4) = 14
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43. Data Types
• So far, we have talked about three data types
– Strings
– Integers
– Reals/decimals (floats)
• Sometimes we have have to be careful about what
types we use
• Fancy words alert: Data type Conversion
– A programming language will have explicit ways to convert
from one data type to another, also called type casting!
– Integer to float: $newFloat = (float) $oldInteger;
– Float to integer: $newInteger = (int) $oldFloat;
– String to float/integer: $number = $stringasnumber;
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44. Gotchas will getcha
• Be careful casting an unknown fraction (float)
to an integer
print (int)( (0.1+0.7) * 10 );
• Result is …
• 7 Why?
• There are many helper functions for casting:
– floor()
– ceil()
– round()
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45. Quiz
• What symbol does PHP use for multiplication?
• How would you get the remainder for 8 / 3?
• How would you get the integer part for 8 / 3?
• What’s another way of calculating 6 * 6 * 6 * 6
in PHP?
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46. • End here.
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47. • Exercises
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48. Exercise 1
• Write a short PHP program, as we just did,
that will print three lines:
– Your name
– Your birth date
– Your favorite color
• My name is James Marcus.
• I was born January 26, 1961.
• My favorite color is blue.
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49. Exercise 2
• Calculate the number of minutes in a week
using variables
– $DaysPerWeek
– $HoursPerDay
– $MinutesPerHour
• How many minutes are there in a week in the
Bilky Way, a near parallel galaxy, if there are
26 hours on a day there?
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