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Introduction to Programming (in JavaScript). David Stotts Computer Science Department UNC Chapel Hill. Everyone have a great break?. How people see me when I tell them I’m a Programmer. How My Mom sees Me. How I see Myself. How I Really Am …. How you now see your May self.
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Introduction to Programming(in JavaScript) David Stotts Computer Science Department UNC Chapel Hill
How you now see your May self Afraid you will become this guy
Ok, Ok… no more fun… this is science Class webpage http://www.cs.unc.edu/~stotts/COMP110-s14/
The Big Six 1. data storage (variables, assignment) 2. data retrieval (expressions, evaluation) 3. repetition (loops) 4. decision making (conditionals) 5. procedure abstraction (functions) 6. data abstraction (arrays)
Model of a Computer No not this…
Model of a Computer • A “model” is a simplification of something complex… an abstraction • We take out some detail to show the basics of something in simple form • Details we remove are irrelevant to the aspects we wish to emphasize or explain in the model
Model of UNC enroll Do 4 or 5 times Pay tuition Take fall classes Take spring classes Get 1.7 mil emails from Alumni Assoc graduate
Model of the Solar System What can we study here? What can we not study?
Scale Model of the Solar System Scale = 1:14,000,000,000 I miss Pluto … don’t you?
Memory Hierarchy • storage size increases • access time increases • cost decreases (per bit) • persistence increases • decreasing frequency of access by processor The “cloud”
Network, cloud USB Disk drives, DVD CPU regs cache Main memory RAM
What happens when you power on your computer? • A minimum amount of information is read from secondary memory into main memory • Control is transferred to that area of main memory; this code reads the core of the OS, called the kernel • The kernel executes the initial process • This process loads a full OS off disk (or cloud) • Called bootstrapping (pulling oneself up by one’s bootstraps)… the computer “boots up” • OS then runs all the other programs you write and use… including JavaScript
Data output wireless, usb, net, print port, sound, video User input Keyboard Mic camera kernel Data to programs Disk CPU Kernel talks to disk CPU runs programs CPU runs full OS kernel OS OS loads CPU runs kernel Main memory RAM
Main Memory Layout Intructions and data all stored in main memory (RAM)
Binary Representation • Internally a computer stores information in binary form, or base 2 • Here’s what a program in memory looks like if you could peek in:
Binary Representation • We group the 0’s and 1’s into chunks to represent different forms of information
Von Neumann revisited Programs and their data all stored together in memory • Some 0’s 1’s chunks stand for numbers • Some stand for characters, text • Some stand for images, videos, etc. • Some stand for memory locations • Some stand for program instructions like “add 2 numbers” or “save register 5 to memory location 2145768”
Von Neumann revisited • Computer sorts it all out during the fetch-execute cycle • When we “program” the computer we express the computations we want in a “high level” language like JavaScript • A compiler or translator converts our human-readable program into a big pile of binary… puts it in memory for the computer to then sort out and run
0, 1 … bits • “0” and “1” are the way computers express information because of physics • A light switch is on, or it is off • A wire has current in it, or it does not • A spot on a disk surface is magnetic, or it is not • A hole is punched in a card, or it is not • “0” is really “absent” or “off” • “1” is really “present” or “on” • We also often think of “0” as false, “1” as true
More on bits • With two physical states in a circuit (on, off) we must build all information from a notation with 2 units, or base 2 • We call this binary • We think of the units as the digits 0 and 1 • A single unit of information is a bitwhich is short for binary digit • We clump bits together into chunks sized by powers of 2
Powers of 2 2^0 is 1 2^4 is 16 2^7 is 128 2^1 is 2 2^5 is 32 2^8 is 256 2^2 is 4 2^6 is 64 2^9 is 512 2^3 is 8 special… we call 8 bits a byte 2^10 is 1024 kilo, 1 kilobit, or 1 Kb 2^20 is 2^10 * 2^10 mega,~ 1 million , 1 megabit, or 1 Mb 2^30 is 1 gigabit or ~ 1 billion bits 2^40 is 1 terabit or ~ 1 trillion bits
Powers of 2 We can do this with bytes too 8 bits is 1 byte 2^10 bytes is 1024 bytes is 1 kilobyte (KB) 2^20 is 1024 * 2^10 bytes is 1 megabyte or 1 MB 2^30 bytes is 1 gigabyte or 1 BG 2^40bytes is 1 terabyte or 1 TB
Binary Representation • Binary for numbers is base 2 • 1 1 0 1 (base 2) is 1 times 2^3 … 8 (base 10) 1 times 2^2 … 4 0 times 2^1 … 0 1 times 2^0 … 1 13 (base 10) add these together
First Program • Here is a Web page with a JavaScript program • Here is the program source code <script type=text/javascript> function simpleFunc( ) { //put your program text below the dashed line //---------------------------------------------- alert("Hello from your first program !"); //---------------------------------------------- //put your program text above the dashed line } </script>
Well Done • You know what a model is • Using the von neumann computer model, you know about the insides of the computer you will program • You have run your first program • You know that computers store information (data, programs) internally in binary form (base 2)
For Next Time • Review math: base 2 and powers of 2 • Read intro, chap. 1 in text • Download first program HTML doc to your PC and make sure you can • edit it, esp. <script> … </script> • make the browser browse it • run the program
